Historical Rules · 14 April 2023
Rule 702.160a
Official source text from the 14 April 2023 Rules release
Prototype is a static ability that appears on prototype cards that have a secondary set of power, toughness, and mana cost characteristics. A player who casts a spell with prototype can choose to cast that card “protoyped.” If they do, the alternative set of its power, toughness, and mana cost characteristics are used. See 718, “Prototype Cards.”