Harper, Eater of Crayons

When Harper enters the battlefield, each
opponent creates a Crayon artifact token that's
all colors.
Whenever Harper attacks, defending player
creates a Crayon artifact token that's all colors,
then, you may pay {x}. If you do, destroy up to X target Crayon artifacts and put X times two
+1/+1 counters on Harper.
Apparently, they taste good.