This UNO chose the path of violence. 

UNO Show 'Em No Mercy is a brutal, ruthless version of the classic UNO card game. In addition to standard action cards like Skip, Reverse, and Draw 2, No Mercy comes with Wild Draw 6, Wild Draw 10, Skip Everyone, Discard All, and the new Wild Color Roulette - a card that forces the next player to choose a color and then draw until they get a card of that color.
 
In addition to new action cards, many popular house rules have been included in the actual rules. Stacking is legal. 7s swap and 0s pass hands. And when you can't play a card, you must draw until you can play.
 
But the biggest change in UNO Show 'Em No Mercy is the Mercy Rule. If you ever have 25 or more cards in your hand, you get kicked out of the game.