2019-07-12
If Vengeful Warchief comes under your control after you've already lost life in a turn, its ability can't trigger during that turn.
2019-07-12
If you pay life to cast a spell or activate an ability, you don't put a +1/+1 counter on Vengeful Warchief until after you've finished casting that spell or activating that ability. You put the counter on Vengeful Warchief before that spell or ability resolves.
2019-07-12
You put only one +1/+1 counter on Vengeful Warchief, no matter how much life you lost.