My Crushing Masterstroke | Magic: The Gathering
Formats My Crushing Masterstroke is Legal in
Official Oracle Text for My Crushing Masterstroke
Official Rulings for My Crushing Masterstroke
6/15/2010 : Any of those permanents that are creatures at the time your declare attackers step begins must attack its owner if able. This includes permanents that became creatures after you gained control of them, such as an animated Chimeric Staff. Any of those permanents that aren't creatures at that time can't attack.
6/15/2010 : If, during your declare attackers step, one of the creatures you gained control of this way is tapped or is affected by a spell or ability that says it can't attack, then it doesn't attack. If there's a cost associated with having that creature attack, you aren't forced to pay that cost, so it doesn't have to attack in that case either.
6/15/2010 : If one of those creatures can't attack its owner that turn due to a spell or ability (such as Chronomantic Escape), you may have it attack another player, attack a planeswalker an opponent controls, or not attack at all. If there's a cost with having that creature attack its owner, you aren't forced to pay that cost, so you may have it attack another player, attack a planeswalker an opponent controls, or not attack at all.
6/15/2010 : If there are multiple combat phases that turn, each of those permanents must attack its owner only in the first one in which it's able to.