Doubling Dice

Doubling Dice enters play with 1 counter on it.
Once per turn, you may choose to reveal a card in
your hand, and force an opponent to do the same.
If the combined converted mana cost of the two
cards is even, deal damage to that opponent equal
to the number of counters on this card, then
double the number of counters. If it's odd,
you discard your chosen card.