Milena Oswald, Storm Raider

Flash (you may cast this spell at any time you could
cast an instant.)
When Milena Oswald enter the Battlefield, put a
-1/-1 counter on each creature your opponents
controls.
Whenever a creature with a -1/-1 counter on it
dies, add {c} to your mana pool. ({c} represents
colorless mana.)
"See ? My plan worked finally"
- Milena Oswald