Cheapest priced copy (Murders at Karlov Manor): $1.49 at Card Kingdom, near mint, their price list as of .
Repulsive Mutation 
Instant · Uncommon · Murders at Karlov Manor · #227
Put X +1/+1 counters on target creature you control. Then counter up to one target spell unless its controller pays mana equal to the greatest power among creatures you control.
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
1 printing · $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Murders at Karlov Manor | 227 | Uncommon | $1.49 | $1.49 |
One ruling from Wizards of the Coast
- 2 February 2024If you control no creatures as Repulsive Mutation is resolving, the amount of mana the target spell's controller must pay to stop their spell from being countered is 0. That player can choose not to pay 0 mana; if they do, the spell will be countered.