Greven gets +X/+0, where X is the amount of life you've lost this turn.
Whenever Greven attacks, you may sacrifice another creature. If you do, you draw cards equal to that creature's power and you lose life equal to that creature's toughness.
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
The sacrificed creature's power and toughness are determined by its last known information before it left the battlefield.
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
A player loses life if they're dealt damage or if they pay life.
Format Legality
Standard
Not Legal
Future
Not Legal
Historic
Not Legal
Timeless
Not Legal
Gladiator
Not Legal
Pioneer
Not Legal
Modern
Not Legal
Legacy
Legal
Pauper
Not Legal
Vintage
Legal
Penny
Not Legal
Commander
Legal
Oathbreaker
Legal
Standardbrawl
Not Legal
Brawl
Not Legal
Alchemy
Not Legal
Paupercommander
Not Legal
Duel
Legal
Oldschool
Not Legal
Premodern
Not Legal
Predh
Not Legal
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