Evil Mook has 4 Attack and 12 Hearts and he is considered a Boss. He requires a sacrifice to be played, the player may choose to pay 500 points or alternatively discard 2 cards with the word "Mook" in their name (example: Mook) from their own field, the opponent's field, their hand or a combination.
He cannot attack a target unless it would reduce it's hearts to zero. This includes directly attacking players. If the opponent plays a card to cancel or reduce damage (or something else that would of made the card survive), the attack will still technically of happened even if the defending card/player is not defeated.
Evil Mook is a very powerful card, but requires a costly ammount to summon. Additionally, Evil Mook can only attack cards and players when he would reduce their hearts to zero with his attack, making him easily countered by some high health cards such as Ceramic Turtle.
However, Evil Mook is still an incredibly useful card for cleaning up and pairs well with other cards with a high attack value.