If, during a player's declare attackers step, a creature is tapped, is affected by a spell or ability that says it can't attack, or hasn't been under that player's control continuously since the turn began (and doesn't have haste), then it doesn't attack. If there's a cost associated with having a creature attack, the player isn't forced to pay that cost, so it doesn't have to attack in that case either.
15-09-2013
wotc
The controller of each attacking creature still chooses which player or planeswalker that creature attacks.
15-09-2013
wotc
The last ability affects creatures that are already attacking when it resolves. Activating it before combat won't affect any creatures that attack later that turn.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.
: Target creature an opponent controls attacks this turn if able.
, 
: Attacking creatures get -1/-1 until end of turn.
Daarken2016-08-26
