Life Seep

Life Seep gradually takes the life out of its victim. If used for as long as possible, the expected result on the victim's end is death. The user normally must be in close proximity of their target, often making contact them as the superpower is being put to work, but there are rare variants that allow it to work from a distance. Strangling someone with your bare hands for long enough is a way to unlock this superpower in real life, though this is a bad idea as murder is illegal. Constrictor snakes like the famous boa and anaconda use Life Seep on their prey in an inescapable full-body hold.

Nested
Parasitic Drain: This is doubly useful to the user than normal, effectively adding on to their own health through that taken from the enemy.

Risks

 * Because the user must be close to their target for a considerably long time to get a kill, they're wide open to escape or counterattacks from the other party.