Whenever you sacrifice a black creature, you may pay 2 life. If you do, each other player sacrifices a creature of their choice.
Whenever you sacrifice a green creature, you may gain 2 life.
Sacrificing a creature that's both black and green will make both abilities trigger. You may put them on the stack in whichever order you want.
12 Jan 2024
Savra itself doesn't let you sacrifice creatures. Its abilities trigger whenever you sacrifice a black or green creature because some other spell, ability, or cost instructed you to do so.