
Whenever you sacrifice a permanent, this creature gets +2/+0 until end of turn.
, Sacrifice another creature or an enchantment: This creature gains first strike until end of turn.
"Mogis is pleased by this offering. Bring him more!"
Illustrated by Steve Prescott
Released on January 24, 2020
The first ability of Slaughter-Priest of Mogis is a triggered ability, not an activated ability. It doesn't allow you to sacrifice a permanent whenever you want; rather, you need some other way of sacrificing permanents, such as its second ability.
Multiple instances of first strike on the same creature are redundant.