The Mimeoplasm

Mana cost: {2}{B}{G}{U}
Type: Legendary Creature — Ooze
Power / toughness: 0 / 0
Set: Commander 2011 Oversized #210 (mythic)

As The Mimeoplasm enters, you may exile two creature cards from graveyards. If you do, it enters as a copy of one of those cards with a number of additional +1/+1 counters on it equal to the power of the other card.

The Mimeoplasm has 12 printings, first in Commander 2011 (2011). EDHREC ranks it #7,482 among Commander cards. It appears most in Indominus Rex, Alpha decks (2,762 on EDHREC). 3 public decks on TCG run it. It has 5 official rulings.

Legality

commander: legal
legacy: legal
vintage: legal
pauper: not legal
modern: not legal
pioneer: not legal
standard: not legal
brawl: not legal

Public decks that run The Mimeoplasm

Devour for Power - Commander 2011, led by The Mimeoplasm
Devour for Power - Commander Anthology Volume II, led by The Mimeoplasm
Grand Larceny - Outlaws of Thunder Junction Commander, led by Gonti, Canny Acquisitor

Commanders that run The Mimeoplasm most

Deck counts from EDHREC.

Often played with The Mimeoplasm

Cards that show up in the same decks on EDHREC.

Rulings

2011-09-22: Treat The Mimeoplasm as though it were the creature card it's copying entering the battlefield. Any "As [this card] enters," "[This card] enters with," and "When [this card] enters" abilities of that creature card will work.
2011-09-22: You choose which one The Mimeoplasm is copying and which one determines how many +1/+1 counters are placed on The Mimeoplasm as The Mimeoplasm enters.
2011-09-22: Specifically, if The Mimeoplasm as a copy of a creature card that enters the battlefield with a number of +1/+1 counters, The Mimeoplasm will enter with those +1/+1 counters and +1/+1 counters equal to the power of the other exiled card.
2011-09-22: You can't choose to exile just one creature card.
2011-09-22: The two creature cards may come from the same graveyard or different graveyards.