Once transformed, it becomes Polukranos, Engine of Ruin, which is a 6/6 with reach and lifelink and reads: Whenever Polukranos, Engine of Ruin or another nontoken Hydra you control dies, create a 3/3 green and white Phyrexian Hydra creature token with reach and a 3/3 green and white Phyrexian Hydra creature token with lifelink. Even without any other hydra creatures, the fact this card will split into two is amazing - but with some clever deckbuilding, it could make your deck unkillable
Its time to go dungeon diving
But the true damage takes place during the second chapter, tapping down all of an opponents creatures and swinging in for a minimum of eight damage
Fill your deck with cheap Elves, sacrifice outlets, and cards that dump creatures into your graveyard
GR Gold Rare Slifer the Sky Dragon X DIVINE Level 10 [ Divine-BeastEffect ] ATK
Pot of Greed is probably the most infamous case of this as mentioned below, being a straightforward card that allows the player to draw 2 more cards