Cheapest priced copy (Gatecrash): $0.35 at Card Kingdom, near mint, their price list as of .
Miming Slime 
Sorcery · Common · RNA Guild Kit · #113
Create an X/X green Ooze creature token, where X is the greatest power among creatures you control.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
3 printings · $0.35 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| RNA Guild Kit | 113 | Common | $0.79 | — |
| Gatecrash | 126 | Uncommon | $0.35 | $0.49 |
| Ultimate Masters | 173 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 7 December 2018The power and toughness of the Ooze token is determined when Miming Slime resolves. It won’t change as the greatest power among creatures you control changes.
- 7 December 2018The value of X is the greatest power among creatures you control when Miming Slime resolves. If you control no creatures at that time, X will be 0, creating a 0/0 Ooze token that will be put into your graveyard as a state-based action (unless something else is raising its toughness).