Cheapest priced copy (Double Masters 2022): $0.49 at Card Kingdom, near mint, their price list as of .
Slimer, Voracious Apparition 
The Mimeoplasm
Legendary Creature — Ooze · 0/0 · Rare · Secret Lair Drop · #1773
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.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
10 printings · $0.49 to $8.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Double Masters 2022 | 254 | Rare | $0.49 | $0.49 |
| Double Masters 2022 | 383 | Rare | $0.59 | $1.49 |
| Double Masters 2022 | 525 | Rare | — | — |
| Commander's Arsenal | 12 | Mythic | — | $1.29 |
| Commander Anthology Volume II | 1 | Mythic | — | $0.99 |
| Commander 2011 | 210 | Mythic | $0.99 | — |
| Commander 2011 Oversized | 210 | Mythic | — | $0.99 |
| Outlaws of Thunder Junction Commander | 234 | Rare | $0.49 | — |
| Secret Lair Drop | 136 | Mythic | $8.49 | — |
| Secret Lair Drop (Slimer, Voracious Apparition) | 1773 | Rare | $4.99 | $3.99 |
5 rulings from Wizards of the Coast
- 22 September 2011Treat 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.
- 22 September 2011You 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.
- 22 September 2011Specifically, 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.
- 22 September 2011You can't choose to exile just one creature card.
- 22 September 2011The two creature cards may come from the same graveyard or different graveyards.