Cheapest priced copy (Kamigawa: Neon Dynasty): $0.39 at Card Kingdom, near mint, their price list as of .
Dragonspark Reactor 
Artifact · Uncommon · Kamigawa: Neon Dynasty · #137
Whenever this artifact or another artifact you control enters, put a charge counter on this artifact.
{4}, Sacrifice this artifact: It deals damage equal to the number of charge counters on it to target player and that much damage to up to one target creature.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.39 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Kamigawa: Neon Dynasty | 137 | Uncommon | $0.39 | $1.49 |
2 rulings from Wizards of the Coast
- 18 February 2022If you target both a player and a creature as you activate the ability, and one of the targets is illegal as the ability resolves, Dragonspark Reactor will deal damage to the remaining legal target. If both targets are illegal, the ability won't resolve.
- 18 February 2022Targeting a creature is optional, but you must choose at least one target player to activate Dragonspark Reactor's last ability.