Wahlia, Reality Fuser

Creature cards in your hand without overlay
have overlay. Its overlay cost is equal to its mana
cost reduced by up to {1}.
(You may discard this card and pay its overlay cost,
when you do exile it overlayed onto target creature.)
Each creature you control has all activated
abilities of cards overlayed onto it and gets
+X/+Y where X is the total power of cards
overlayed onto it and Y is the total toughness of
cards overlayed onto it.