Cheapest priced copy (Double Masters 2022): $0.35 at Card Kingdom, near mint, their price list as of .
Might of Old Krosa 
Instant · Uncommon · The List · #TSP-204
Target creature gets +2/+2 until end of turn. If you cast this spell during your main phase, that creature gets +4/+4 until end of turn instead.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
5 printings · $0.35 to $4.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Double Masters 2022 | 153 | Common | $0.35 | $0.49 |
| Modern Masters 2017 | 130 | Uncommon | $0.35 | $0.49 |
| The List | TSP-204 | Uncommon | $0.35 | — |
| Time Spiral | 204 | Uncommon | $0.39 | $4.49 |
| Time Spiral Remastered | 217 | Uncommon | $0.39 | $0.99 |
One ruling from Wizards of the Coast
- 19 March 2021If an effect copies Might of Old Krosa while it's on the stack, the copy will give the creature only +2/+2, even if the original spell was cast during your main phase. This is because the copy is created on the stack and wasn't cast at all.