Grab the Infinite

Grab the Infinite can't be countered.
Discard a card:Choose a person outside the game.
Until end of turn,that person chooses a red card
from the CUBE,then you put that card in your hand.
When you cast that card,you may spend mana as though it were mana of any color.
At the beginning of your next end step,
exile that card from your hand.