polymerization

Polymerization is a normal-type "spell card":https://yugioh.fandom.com/wiki/Spell_Card in the yu-gi-oh! trading card game. This card allows its user to "Fusion Summon":https://yugioh.fandom.com/wiki/Fusion_Summon one "Fusion Monster":https://yugioh.fandom.com/wiki/Fusion_Monster from their "Extra Deck":[https://yugioh.fandom.com/wiki/Extra_Deck] by fusing monsters from their hand or their side of the field. As it is the main way to summon most of the powerful Fusion Monsters, it is a staple in the deck of many main characters, including Muto Yugi and Yuki Judai.