Cheapest priced copy (Dominaria United Commander): $0.99 at Card Kingdom, near mint, their price list as of .
O-Kagachi, Vengeful Kami 
Legendary Creature — Dragon Spirit · 6/6 · Mythic · Mystery Booster 2 · #138
Flying, trample
Whenever O-Kagachi deals combat damage to a player, if that player attacked you during their last turn, exile target nonland permanent that player controls.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
3 printings · $0.99 to $1.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2017 | 45 | Mythic | — | $1.79 |
| Dominaria United Commander | 164 | Mythic | $0.99 | — |
| Mystery Booster 2 | 138 | Mythic | $0.99 | $0.99 |
3 rulings from Wizards of the Coast
- 25 August 2017If O-Kagachi deals lethal damage to a blocking creature and also deals damage to its controller, that blocking creature is destroyed before a target is selected for O-Kagachi's last ability. It can't be exiled.
- 25 August 2017A player attacked you if that player declared a creature as an attacking creature and that creature is attacking you. If that player attacked only planeswalkers you control, that player didn't attack you. If that player's creatures were attacking you only because they were put onto the battlefield attacking or only because you were reselected as the player they were attacking, that player didn't attack you.
- 25 August 2017O-Kagachi's last ability exiles only one nonland permanent, no matter how many creatures attacked you or how many times that player attacked you during their last turn.