Cheapest priced copy (Commander Masters): $0.35 at Card Kingdom, near mint, their price list as of .
Heart-Piercer Bow 
Artifact — Equipment · Common · Commander Masters · #390
Whenever equipped creature attacks, this Equipment deals 1 damage to target creature defending player controls.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
4 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Masters | 390 | Common | $0.35 | $0.49 |
| Jumpstart 2022 | 773 | Common | $0.35 | — |
| Khans of Tarkir | 221 | Uncommon | $0.35 | $0.49 |
| Core Set 2020 | 228 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 12 July 2019Heart-Piercer Bow (not the equipped creature) is the source of the triggered ability and the source of the damage. This means that a creature with protection from green may be targeted even if Heart-Piercer Bow is equipped to a green creature, but a creature with protection from artifacts may not.
- 28 July 2023If a creature is attacking a planeswalker, the controller of that planeswalker is the defending player. If a creature is attacking a battle, the protector of that battle is the defending player.