At the beginning of your end step, exile up to one target creature card from your graveyard. If you do, seek a creature card with mana value equal to the mana value of that card plus one. That card perpetually gains menace.

Whenever Stubborn Burrowfiend becomes saddled for the first time each turn, mill two cards, then Stubborn Burrowfiend gets +X/+X until end of turn, where X is the number of creature cards in your graveyard.

Saddle 2 (Tap any number of other creatures you control with total power 2 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)

Choose target creature you control and target creature you don't control. If you cast this spell during your main phase, the creature you control gets +1/+1 until end of turn. Then those creatures fight each other. (Each deals damage equal to its power to the other.)