Xanagen, to be Born Again

Haste, Trample
Xanagen attacks each turn if able.
Xanagen enters the battlefield with a +1/+1
counter on it for each mana spent to cast it.
At the beginning of your post combat main phase
gain {c} equal to the combat damage dealt by a
creature of your choice to an opponent this turn.
Spend this mana only to cast creature spells.