"Polymerization" ( (ゆう) (ごう) Yūgō, lit. "Fusion") is an archetype of mostly Spell Cards used to Fusion Summon Fusion Monsters. It is closely tied to the "Fusion" archetype.

While many cards with "Fusion" in their names are actually in the "Polymerization" archetype instead (or are in both despite only having "Fusion" in their name), all support cards for this archetype also support the "Fusion" archetype at the same time, making this a non-issue. "Diffusion Wave-Motion" is not a "Fusion" nor a "Polymerization" card due to its Japanese name, so it includes an archetype-exclusion condition to indicate this.

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