A player loses life if they're dealt damage or if they pay life.
2019-08-23 • wotc
Greven checks for how much life you lost, not how much your life total has changed. If you lost 4 life but also gained 6 life, you still lost 4 life and Greven gets +4/+0.
2019-08-23 • wotc
The sacrificed creature's power and toughness are determined by its last known information before it left the battlefield.
2019-08-23 • wotc
You sacrifice a creature (or choose not to), draw cards, and lose life all while Greven's triggered ability is resolving. Nothing can happen in between, and no player may choose to take actions.
2019-08-23 • wotc