Corpse Cur

The enters-the-battlefield clause is what marks this as an infect-deck card rather than an infect-creature card. A 2/2 with infect for four mana is a poor rate on its own; poison decks live and die on cheap, evasive threats, and this is neither cheap nor evasive. What it offers instead is graveyard recursion that only an infect strategy can use: every removal spell or chump block your opponent spends on your poison creatures becomes a card you can buy back, turning the attrition math in favor of the player who is already counting to ten. That self-referential design (an infect creature that retrieves other infect creatures) is the kind of glue a corner-case mechanic needs to function as a deck rather than a pile of unrelated bodies. The Phyrexian Dog flavor frames it as exactly that role: a scavenger that drags the fallen back to the front line, which is also a tidy description of what the card does at the table. Outside a build committed to the -1/-1-counter-and-poison axis it does nothing worth the four mana, and that narrowness is the point; it was made to reward going all-in on a payoff structure that otherwise had little redundancy.