At the beginning of your precombat main phase, add {B} for each charge counter on Altar of Shadows. {7}, {T}: Destroy target creature. Then put a charge counter on Altar of Shadows.
2004-10-04
The precombat main phase is the first main phase of the turn. All others are postcombat main phases, even if they technically occur before combat.
2004-12-01
You put the counter on Altar of Shadows even if the creature regenerates.