Sightless Ghoul

The "can't block" clause is the whole bargain here. Undying wants to be sticky, and a recurring 2/2 body that comes back as a 3/3 would normally be a defensive nuisance, so the design pays for the resilience by stripping the card of any ability to hold the ground. What you get back is a creature that only ever points forward: it attacks, it dies, it returns one size larger, and it stops nothing on its way out. That asymmetry makes it a different tool than most undying creatures, which lean on the mechanic to grind out attrition wars from both sides of the board. This one is built strictly for the aggressor's side of the equation, where the second life and the counter translate into pressure rather than insurance. The interaction with sacrifice effects is where it earns its keep: because its first death leaves no +1/+1 counter behind, it satisfies the undying condition cleanly, returning ready to be fed again, and the can't-block restriction costs a deck that intends to throw it away nothing at all. Four mana for a 2/2 with this much text is a slow rate on its face, but the body was never the point; the point is a Zombie that refuses to stay dead exactly once, and only ever on offense.