mtg commander legal cards in commander, Rules Text: search your library, land, into your hand, onto the battle..., 13 mtg pioneer legal cards Amazon.com:

As a great final touch, these croak counters remain on exiled cards even if an opponent removes Grolnok, meaning they can still be cast once Grolnok is replayed from the command zone later

Hapatra, Vizier of Poisons Hapatra, Vizier of Poisons is all about those -1/-1 counters, and its ability to create tokens and other synergies with them lands it pretty high

(When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.) This creature has haste as long as you control a red creature

The downside is that the card has a chance of dealing three damage to you on your upkeep, but this downside is far outweighed by the absolutely ludicrous upside

Fantastic EDH Zombie Token maker, only available in Commander 2014, Jumpstart and Commander Collection: Black