Bloodbriar

Creature — Plant Elemental

Whenever you sacrifice another permanent, put a +1/+1 counter on Bloodbriar.

2/3

2020-08-07:
Bloodbriar's ability 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.
2020-08-07:
If you sacrifice a permanent as part of casting a spell or activating an ability, Bloodbriar's ability will resolve before that spell or ability.
2020-08-07:
A legendary permanent that is put into a graveyard because of the “legend rule” isn't sacrificed.