Evolution Monsters (進化モンスター Shinka monsutā) are monsters that reside within the Main Deck identified with a Silver Border. They are Evolution Summoned by sending monsters on your side of the field with the "Devolved" monster drawing power from other monsters to attain a new form.
Evolution Summoning an Evolution Monster requires you to target one monster on your side of the field, the "Devolved" monster, and then send 2 other monsters to the Graveyard and Special Summon the Evolution Monster from your Hand.
Trivia[]
Evolution Monsters originally were summoned from the Extra Deck, but were changed on the basis of being overpowered, and the introduction of Link Summoning and the March 26 2017 rules.