Problem is that it doesn't survive many combats to become the enchantment. Only a 1 power creature wouldn't kill it.Limited said:Maybe what the Stirges need, is simplification:
Stirge 1BB 1/2
Whenever <THIS> deals damage to a creature, <THIS> becomes an enchantment enchanting that creature, and has "At the beginning of your upkeep, put a -1/-1 counter on enchanted creature"
It still leaves a lot of room for tricks, and turns the card into conditional (and optional) removal.