+ Create a Fusion Monster +

[The Nepfessor]

Tank Dragon
Level 5 LIGHT Dragon/Fusion/Effect
2600/1000
1 Machine monster + 1 Dragon monster
When this card destroys an opponent's monster by battle and sends it to the GY: You can Special Summon that monster to your field in Defense Position, and if you do, it is treated as a Machine monster. If this card would be destroyed by battle or card effect, you can destroy 1 card you control instead.

N/C: Another Predaplant Fusion Monster.

[Flash Flyer - Sakura]

Predaplant Rafflesia Ouroboros
Level 10 | DARK | Plant | Fusion | Effect
3300/2500
3 DARK monsters with different names on the field
Must be Fusion Summoned, or Special Summoned by sending the above monsters your opponent controls with a Predator Counter(s) (in which case you do not use "Polymerization"). When this card is Special Summoned: You can target up to 3 monsters in your opponentʻs GY; banish those targets, and if you do, this card gains ATK equal to their combined ATK. This card can attack all monsters your opponent controls once each.

Yeah...not gonna look up carnivorous plants right now, so you get Rafflesia again.

====
Let's make a (somewhat) generic Zombie Fusion

[Draconus297]

Underworld Overseer
DARK - Level 8 - Zombie/Fusion/Effect - 4000/0
2 or more Zombie monsters with a combined ATK of 4000 or less
Cannot be destroyed or targeted by card effects, except the effects of this card. Battle damage your opponent takes from battles involving this card is halved. If this card destroys your opponent's monster by battle: Destroy 1 card on the field. While this card is face-up on the field, if you control "Zombie World", your opponent cannot Summon monsters from their own Graveyard.

1. Create an "Ascent of Fusion" target- a non-Effect Fusion with two named Materials that you'd want to Foolish from the Deck, then immediately revive.
2. Make a Fusion with a sort of revival loop effect- think something along the lines of Garunix returning every turn, Lightpulsar and Dr. Red being able to eternally bring one another back, Number C101 being effectively immortal so long as 101 is in the Graveyard, etc.
3. Create a semi-generic Insect Fusion.

[The Nepfessor]

Insectoid Antennant
Level 7 EARTH Insect/Fusion/Effect
2300/1500
1 Insect monster + 1 Level 4 or lower monster
Cards in your Field Zone cannot be destroyed by card effects. You can activate 1 Continuous Trap the turn it was Set.

Yeah...backlog cards from all over 2014. At its finest.

N/C: A Fusion of 2 Ritual Monsters of a purely Ritual archetype (e.g. Gishki, Nekroz, Megalith).

[Flash Flyer - Sakura]

Nekroz of Five-Headed
Level 12 | WATER | Dragon | Fusion | Effect
5000/5000
3+ "Nekroz" Ritual Monsters with different names
Must be Fusion Summoned with the above monsters. If this card is Fusion Summoned: You can destroy cards on the field, up to the number of monsters used to Fusion Summon this card. Unaffected by your opponent's card effects. If this card was Fusion Summoned using 5 monsters as material, apply these effects.
● Your opponent cannot Tribute monsters you control, also they cannot use monsters you control as material for a Summon.
● When your opponent Summons a monster OR activates a card or effect (Quick Effect): You can banish 1 "Nekroz" card from your hand or GY; negate the Summon or activation, and if you do, banish it.

While it is possible to summon this from the hand with all 5 monsters, that would require that:
- You go second to get the added card during Draw Phase.
- You actually have 5 Nekroz Rituals in hand to do it.
- Draw Polymerization or have some way to Fusion Summon (i.e. opponent plays Fusion Gate or something)
- Don't get Strike'd because opponent did it.

====
Make a Fusion Monster based on pre-ARC-V archetypes.

For general reasons, Valkyrie and stuff that got released way later, but did debut in the anime before their official releases count in this category.

[Draconus297]

Cannon Barrel Dragon
DARK - Level 8 - Machine/Fusion/Effect - 3000/2600
1 "Barrel Dragon" monster + 1 DARK Machine monster
This card on the field cannot be used as Material for a Summon. Once per turn, during the Battle Phase (Quick Effect): You can toss 3 coins; banish a number of cards on the field equal to the number of Heads. If you tossed 3 Heads for this card's effect, you can Special Summon 1 DARK Machine monster from your hand or Graveyard. During a turn in which a coin(s) was tossed, this card gains 1 additional attack on a monster for each Heads that was tossed.

1. An "Ascent of Fusion" target. Try to think of two monsters with different names that you want to either touch the Graveyard or instantly dump to Summon from the Graveyard.
2. Semi-generic self-reviving monster.
3. Characters prior to ZeXal had a bad habit of running a bunch of random monsters that weren't exactly connected to any real archetype. Create a Fusion for two of these bosses that were run by the same character, or for two characters who were on the same side.

[Flash Flyer - Sakura]

I'm going to be somewhat lazy and just make a Fusion for Ruka/Luna's stuff.

Sunlight & Regulus, Servants of Ancient Fairy
Level 7 | LIGHT | Beast | Fusion | Effect
2650/1500
"Regulus" + "Sunlight Unicorn"
Must first be Fusion Summoned with the above monsters. Other LIGHT and Dragon Synchro Monsters you control cannot be targeted or destroyed by an opponent's card effects, also they cannot be Tributed. Once per turn: You can target 1 Spell Card in your GY; shuffle it into the Deck. Once per turn: You can excavate the top card of your Deck, and if it is a Spell/Trap Card, you can add it to your hand. Otherwise, shuffle it into the Deck.

Well, Regulus actually has a role here with Ancient Fairy Dragon. Sunlight Unicorn is debatable, but Ruka used it so here you go.

====
Requires different Extra Deck types as material.

[Nyx Silvercrown]

Tankroid
EARTH - Level 8 - Machine/Fusion/Effect - 2500/3000
2 "roid" monsters
Must first be either Fusion Summoned, or Special Summoned by sending the above cards you control (in which case you do not use "Polymerization"). You can send 1 "roid" card from your hand or Deck to the GY; destroy 1 card your opponent controls, and if it was a monster, inflict damage to your opponent equal to its ATK. Cannot attack the turn you activate this effect. You can only activate this effect of "Tankroid" once per turn, and only once that turn.

Next:
One that requires a certain monster as one of the Fusion materials, but only that monster. The other material can be whatever you desire.

[Flash Flyer - Sakura]

(The prompt was intended to require the monsters to literally be different ED types, though since 'roids do encompass Fusion and Synchro, suppose it counts.)

Stardust Chaos Dragon
Level 10 | LIGHT | Dragon | Fusion | Effect
3300/2500
"Stardust Dragon" + 1 LIGHT monster + 1 DARK monster
Must first be Fusion Summoned or Special Summoned from your Extra Deck by sending the above monsters on the field to the GY (in which case you do not use "Polymerization"). Cards you control cannot be destroyed by card effects. Once per turn, when a card or effect is activated OR a monster is Summoned (Quick Effect): You can banish this card; negate the Summon or activation, and if you do, banish that card. During the End Phase, if this effect was activated (and was not negated): You can Special Summon this banished card.

Chances are that you'll have to steal the non-Stardust components from the opponent, well, least the DARK portion anyway.

==========
Legacy support Fusion for any real archetype/series, etc that you want.

[Draconus297]

R-Genex Ally Distributor
DARK - Level 4 - Machine/Fusion/Tuner/Effect - 1200/2500
2 "Genex" monsters
If you Synchro Summon using 1 or more "Genex" monsters as Material: Increase this card's Level by 1. Once per turn (Quick Effect): You can change this card's Attribute to any desired Attribute. Once per turn, you can reduce this card's Level by any amount: Special Summon 1 non-Fusion "Genex" monster from your Graveyard whose Level is exactly equal to the amount this card's Level was reduced by. If this card is in your Graveyard, and a "Genex" monster(s) is sent to your Graveyard (Quick Effect): You can Special Summon this card from your Graveyard, then destroy 1 card each player controls. You can only activate this effect of "R-Genex Ally Distributor" once per turn.

1. An "Ascent of Fusion" target, as described above.
2. Semi-generic self-reviver.
3. Make something with a similar control effect to Slifer the Sky Dragon.

[Flash Flyer - Sakura]

Emissary of the Sky Dragon
Level 10 | LIGHT | Spellcaster | Fusion | Effect
3000/2500
2 monsters, including a Level 7 or higher Dragon monster
Must be Fusion Summoned, or Special Summoned (from your Extra Deck) by sending the above monsters on either player's field to the GY (in which case you do not use "Polymerization"). Your DIVINE monsters are unaffected by an opponent's card effects, also your opponent cannot Tribute them. If your opponent Summons a monster(s): That monster(s) loses 1000 ATK/DEF, then if its ATK or DEF has been reduced to 0 as a result, destroy it. and if you do, inflict 800 damage to your opponent for each.

======
Make a monster with an alternative way to Fusion/Special Summon it.

[Draconus297]

Avaricious Golem of Darkness
DARK - Level 10 - Fiend/Fusion/Effect - ?/?
1 monster with an original ATK of "?" + 1 or more DARK Effect monsters
If your opponent activates a monster effect from their hand while you control a monster with an original ATK of "?": You can negate that effect, then Fusion Summon this card using appropriate Materials from either field, including banishing that monster whose effect was activated (which is treated as a DARK monster). You can only Summon 1 "Avaricious Golem of Darkness" per turn this way. This card's ATK and DEF are equal to its Level x300. If this card destroys your opponent's monster by battle: Increase this card's Level by the Level of the destroyed monster, or double the Rank or Link Rating of the destroyed monster. This card's maximum number of attacks per Battle Phase is equal to the number of DARK monsters used as Material for its Fusion Summon. This card's attacks and effects cannot be negated.

1. An "Ascent of Fusion" target, as described above.
2. Semi-generic self-reviver.
3. A Miracle Synchro Fusion target whose effect points you in the direction of a specific Synchro, but that is semi-generic.

[Flash Flyer - Sakura]

Ascent of Fusion is a non-Effect Fusion that can dump named materials you want to revive.

Armory Dark Magician
Level 8 | DARK | Spellcaster | Fusion
2800/2600
"Dark Magician" + "Magician's Robe"

===
IDK if that works out, so gonna try theme 2 as an extra.

Seikenmaru, Blade of the Royal Guard
Level 10 | LIGHT | Beast | Fusion | Effect
3300/2800
1 Beast with 2500 or more original ATK + 1 Warrior monster
Your opponent cannot target or destroy this Fusion Summoned card with card effects, also control of this card cannot switch. This card can attack all monsters your opponent controls once each. If this card attacks, your opponent cannot activate cards or effects until the end of the Damage Step. If this card is destroyed and sent to the GY: You can discard 1 card; Special Summon this card.

(Just for the record, Seikenmaru is the name I gave my Zacian in-game so....yeah)

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1. Give Deck that lacks a Fusion (but is capable of running Poly or something) one.
2. Monster with Z-ARC esque conditions (requires 1 each of different summon mechanics, but you can choose how to go about this)

[Draconus297]

Yup! Ascent of Fusion is Future Fusion for non-Effect Fusions, and revives all of the named Materials when a non-Effect Fusion is Summoned. Blue-Eyes Ultimate is probably the best target, but Sanwitch is hilariously solid.

Red Nova Resonator King
FIRE - Level 5 - Fiend/Fusion/Effect - 1800/2100
2 "Resonator" monsters
Once per turn, you can also Fusion Summon this card by Tributing appropriate Materials you control. If this card is Special Summoned: You can banish 1 monster from your opponent's field or Graveyard whose Level, Rank, or Link Rating is 4 or lower, then reduce this card's Level by the Level, Rank, or Rating of that banished monster. If this card is sent from the field to the Graveyard by a card effect or as Synchro Material: You can Special Summon up to 2 monsters who fulfill 1 or more of the following criteria:
●Level 3 or lower "Resonator" monster
●FIRE Fiend "Red" monster
●DARK Dragon Synchro monster
You can only activate each effect of "Red Nova Resonator King" once per turn.

1. A Miracle Synchro Fusion target whose effect points you in the direction of a specific Synchro, but that is semi-generic.
2. Allow it to search or recoup a named Spell upon Summon.
3. Retrain a difficult-to-Summon Main Deck boss as a Fusion.

[Flash Flyer - Sakura]

Gate Guardian, the Labyrinth Master of Elements
Level 11 | DARK | Warrior | Fusion | Effect
3750/3400
"Sanga of the Thunder" + "Kazejin" + "Suijin"
Must first be Fusion Summoned, or Special Summoned by banishing the above monsters you control and/or from your GY (in which case you do not use "Polymerization"). Your opponent cannot target or destroy this Fusion Summoned card with card effects. This card can make a second and third attack during each Battle Phase, also if it attacks, your opponent cannot activate Spell/Trap Cards until the end of the Damage Step.

Yeah, Gate Guardian kinda sucks so let's make it worth your while summoning this one (which is somewhat similar to the anime/manga version)

=======
1. Requires a Ritual Monster as material.
2. Monster with Z-ARC esque conditions (requires 1 each of different summon mechanics, but you can choose how to go about this)

[Draconus297]

Interdimensional Spacetime Sorcerer
WIND - Level 9 - Spellcaster/Fusion/Effect - 2600/2600
1 Ritual monster + 1 Synchro monster + 1 Xyz monster
Must be Fusion Summoned. If this card is Fusion Summoned, you can target either this card's Synchro monster or Ritual monster Material in either Graveyard, and banish the other: This card gains ATK equal to the ATK of the target, and the effects and original name of the banished monster (this card is still treated as "Interdimensional Spacetime Sorcerer"). If your opponent activates a card or effect: You can negate the activation, then, if the card whose effect was activated sent a monster to the Graveyard for its effect, you can Special Summon that monster to your field. You can activate this effect a maximum number of times per turn equal to the number of Xyz Materials that were attached to this card's Xyz monster Material. You can only control 1 "Interdimensional Spacetime Sorcerer".

There's lots of combinations to go for with Ritual monster/Synchro monster ATK and effects, although if you're using a Ritual monster for the effect, chances are it's Relinquished (nom), Sapphy (DRAW MORE CARDS), Lord of the Red (quick pops), a Herald (NEGATE NEGATE NEGATE), or something with a lot of protection. Synchros, though, you've got all manner of effects to go for. Remember, though, that you don't get anything from using Borreload Savage but the stats, because that effect triggers on Synchro Summon.

1. A Miracle Synchro Fusion target whose effect points you in the direction of a specific Synchro, but that is semi-generic.
2. Allow it to search or recoup a named Spell upon Summon.
3. Give it a named Material that you wish was easier to search, so you can use Fusion Conscription.

[Flash Flyer - Sakura]

Evil HERO Spatial Inferno
Level 7 | FIRE | Fiend | Fusion | Effect
2500/2000
1 "Evil HERO" monster + 1 Fiend monster
Must first be Special Summoned with "Dark Fusion". If this card is Special Summoned: You can add 1 "Dark Fusion", "Supreme King's Castle" or 1 Spell/Trap Card that specifically lists either of them in its text from your Deck or GY to your hand. If this card destroys a monster by battle, or is destroyed by an opponent's card: You can destroy 1 monster your opponent controls, then inflict damage to your opponent equal to its ATK. You can only use each effect of "Evil HERO Spatial Inferno" once per turn.

(Neos went to the dark side.)

====
1. Retrain an old DM/GX-era Fusion that lacks an effect (ergo, give the new one an effect or something)
2. Fusion for any AGM archetype.
3. "Volcanic" monster

[Draconus297]

Karbonala M-Warrior
EARTH - Level 4 - Warrior/Fusion/Effect - 1500/1200
2 non-Effect EARTH Warrior monsters
This card can make up to 2 attacks per Battle Phase. If this card destroys your opponent's monster by battle: Banish the destroyed monster, and increase this card's ATK by the original ATK of that banished monster. Once per turn, you can banish 1 non-Effect Warrior monster from your Graveyard (Quick Effect): Target 1 Effect monster your opponent controls; negate the effects of the target, also its ATK and DEF become the respective ATK/DEF of the banished monster.

1. A Miracle Synchro Fusion target whose effect points you in the direction of a specific Synchro, but that is semi-generic.
2. Give it a named Material that you wish was easier to search, so you can use Fusion Conscription.
3. Give a boss that lives in the Main Deck a more accessible Fusion counterpart.

[Flash Flyer - Sakura]

I already made Gate Guardian a Fusion counterpart, so let's do Valkyrion, I guess.

Valkyrion Omega the Magna Warrior
Level 8 | EARTH | Machine | Fusion | Effect
3500/3850
"Alpha the Magnet Warrior" + "Beta the Magnet Warrior" + "Gamma the Magnet Warrior"
Must first be Fusion Summoned or Special Summoned (from your Extra Deck) by sending the above monsters you control to the GY (in which case you do not use "Polymerization"). If this card battles an opponent's monster, your opponent cannot activate cards or effects until the end of the Damage Step. If this Fusion Summoned card, or this card that was Special Summoned by its own effect, is sent to the GY by an opponent's card: You can Special Summon 3 "Magnet Warrior" monsters with different names from your hand, Deck or GY, then you can add 1 "Magna Warrior" monster from your Deck or GY to your hand.

====
1. "Acceleranimal" monster
2. Contact Fusion
3. Fusion Monster that can send its materials from the Deck to the GY for its summon

[Draconus297]

Red-Eyes Thousand Metal Dragon
DARK - Level 7 - Dragon/Fusion/Effect - 2400/2000
"Black Metal Dragon" + 1 Level 4 or lower "Red-Eyes" monster
At the start of your opponent's Battle Phase, if you control at least 1 of this card's Fusion Material: You can Fusion Summon this card by sending appropriate Materials from your field, hand, and/or Deck to the Graveyard. You can only Summon 1 "Red-Eyes Thousand Metal Dragon" per turn this way. Cannot be destroyed or targeted by card effects during the turn it is Summoned, and the effects of "Red-Eyes" cards cannot be negated until the second End Phase after this card's Summon. Once per turn, if a "Red-Eyes" monster is Summoned: Reduce the ATK of all monsters your opponent controls by half the ATK of the Summoned monster, then destroy all monsters your opponent controls with 0 ATK. Once per turn: You can Special Summon 1 "Red-Eyes" monster, or Level 1 DARK Dragon monster, from your hand or Graveyard, except "Red-Eyes Thousand Metal Dragon".

1. A Miracle Synchro Fusion target whose effect points you in the direction of a specific Synchro, but that is semi-generic.
2. Give it a named Material that you wish was easier to search, so you can use Fusion Conscription.
3. Make a "Fusion because no other mechanic works" kind of monster, along the lines of Critias Fusion monsters or Masked HERO monsters.