Treacherous Pit-Dweller

Undying is normally a clean upside: a creature dies, comes back bigger, and the +1/+1 counter is the only brake on an infinite loop. Here that keyword has been wired into a trap. The donation clause fires whenever this enters from a graveyard, and undying's return is exactly that kind of reentry, so the textbook undying play (block, die, come back as a 5/4) hands the 5/4 straight to an opponent. The very mechanic built to make creatures harder to answer turns this one into a gift the moment it does what undying creatures are supposed to do.

The design collapses to a single puzzle: bank the aggressive 4/3 body without ever letting the graveyard-return trigger resolve on the wrong side of the table. The clean lines are to ride it as a beater you intend to keep on the board, or to answer it with exile rather than anything that mills, sacrifices, or otherwise routes it through the graveyard. Suppression is tricky here, because the effect that shuts off the enter trigger has to leave the death trigger alone: something like Torpor Orb stops enter-the-battlefield abilities, so the donation clause never resolves, yet undying still triggers on death; a blanket death-trigger hoser would just stop the return entirely and give you nothing. A 4/3 for two beats the curve, so the rate is real. It arrives priced like a present with the receipt stapled to the back, payable in vigilance about exactly how this demon leaves play.