Goblin Diplomats

The controller of each creature still decides which player or planeswalker that creature attacks.

Wotc — July 01, 2013

Creatures that enter the battlefield (or noncreature permanents that become creatures) after the ability resolves are affected by the ability and must attack if able.

Wotc — July 01, 2013

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.

Wotc — July 01, 2013