At the beginning of your precombat main phase, add for each charge counter on Altar of Shadows. , : Destroy target creature. Then put a charge counter on Altar of Shadows.
Legalities
Not Legal
Standardbrawl
Brawl
Future
Pauper
Alchemy
Pioneer
Historic
Standard
Gladiator
Oldschool
Premodern
Historicbrawl
Paupercommander
Explorer
Timeless
Legal
Duel
Penny
Legacy
Modern
Vintage
Commander
Predh
Oathbreaker
Rulings
2004-12-01
You put the counter on Altar of Shadows even if the creature regenerates.