My Crushing Masterstroke

Each of those permanents attacks its owner if able, not necessarily the player you gained control of it from.

Each of those permanents that is a creature 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. Any of those permanents that aren't creatures at that time can't attack.

If, during your declare attackers step, one of the permanents you gained control of this way that's a creature 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.