Whenever a player sacrifices a creature, you may put a +1/+1 counter on this creature.
Mortician Beetle’s ability triggers whenever any player, including you, sacrifices a creature because some other spell, ability, or cost instructed the player to do so. Mortician Beetle itself doesn’t allow you to sacrifice any creatures.
If a creature is sacrificed as a cost to cast a spell or activate an ability, Mortician Beetle’s ability resolves before that spell or ability.
