Whirling Undine

Any -1/-1 counters on Whirling Undine remain
as it enters or leaves the graveyard.
Crippling Shot — When Whirling Undine enters
the battlefield, put X -1/-1 counters on target creature, where X is its power.
Regenerate — Whenever you cast a spell, you may
return Whirling Undine from your graveyard
to the battlefield with a -1/-1 counter on it.