Doomslayer, Blessed

Haste, Vigilance, Menace
This spell costs {1} less to cast for each creature
that died this turn.
In your post-combat main phase, for each creature
that died this turn and was dealt damage by Doomslayer, Blessed, add one mana of any color.
Sacrifice a demon: Doomslayer, Blessed gains indestructible until end of turn.