Eternal youth and immortality, but it must be taken

You’re able to rejuvenate yourself and heal any and all wounds/diseases/missing limbs, while also becoming or staying young. But in order to do any of this, you have to drain another person, killing them. Once you start draining, you can’t stop until the person is dead.

You live normally as you are now, but you suddenly have the ability to lay your hand on somebody and purposefully absorb their life into yours, completely healing your body and bringing it to its absolute peak shape. Sucking old people is less effective as they have less life to take. If you refuse to absorb anybody or decide you don’t want to anymore, you will age normally and heal naturally. Absorbing somebody young while on your deathbed will completely restore you to your peak form, and you will age as if you were 22 again.

How you dispose of the bodies and stay secretly immortal is all on you.