Mangled Stalker

Painborn (Each 1 life you pay while casting this
pays for {1}. It enters the battlefield with a -1/-1 counter on it for each 1 life paid this way.)
Skulk (This creature can't be blocked by creatures with greater power.)
Whenever Mangled Prowler attacks and isn't blocked, You may pay {b}. If you do, remove a
-1/-1 counter from Mangled Stalker.