Tiamat [Dungeons & Dragons: Adventures in the Forgotten Realms] SM81 the equipped monster's ATK becomes

the equipped monster's ATK becomes half its original ATK

You can only use this effect of “Sinister Serpent” once per turn

cannot be activated

Other creatures you control get +1/+1 as long as you've completed a dungeon

Set: XY: Evolutions Type: Fire Rarity: Ultra Rare Retreat cost: Colorless

Tiamat [Dungeons & Dragons: Adventures in the Forgotten Realms] SM81 the equipped monster's ATK becomesSet: Dungeons & Dragons: Adventures in the Forgotten Realms Type: Legendary Creature Dragon God Rarity: Mythic Cost: {2}{W}{U}{B}{R}{G} Flying When Tiamat enters the battlefield, if you cast it, search your library for up to five Dragon cards not named Tiamat that each have different names, reveal them, put them into your hand, then shuffle. "My children will rule over all!"