It's a hard truth. but UNO has officially confirmed that +4 or +2 cards cannot be stacked at all. The card game company issued a post on Twitter yesterday confirming that the move has in fact been illegal all along and that the company knows you’ve been trying to pull it off sneakily. Apparently, it a player puts down a +4 card, the next player must simply draw four cards and skip their turn. No stacking allowed.