Cheapest priced copy (Tarkir: Dragonstorm): $0.35 at Card Kingdom, near mint, their price list as of .
Delta Bloodflies 
Creature — Insect · 1/2 · Common · Tarkir: Dragonstorm · #77
Flying
Whenever this creature attacks, if you control a creature with a counter on it, each opponent loses 1 life.
Legal inCommanderBrawlStandardPioneerModernLegacyVintagePauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Tarkir: Dragonstorm | 77 | Common | $0.35 | $0.49 |
One ruling from Wizards of the Coast
- 4 April 2025Delta Bloodflies’s last ability checks at the moment it would trigger to see if you control a creature with a counter on it. If you don’t, the ability won’t trigger at all. If it does trigger, the ability will check again as it tries to resolve. If you don’t control a creature with a counter on it at that time, the ability won’t resolve and none of its effects will happen.