I was DMing for my group last weekend, and during the session I had a monster do something I'm not quite happy with.
To set the scene: A group of goblins led by a bugbear spot the party over some rolling hills. The party, on their horse-drawn cart, move to engage. During the altercation, the bugbear disappears and the goblins are summarily defeated. Two PC's head off in the direction they last saw the bugbear, and the other three begin looting. Suddenly, the bugbear jumps out from behind the party's cart, and brains one of the (non-combat trained, standard bestiary) horses. With a successful acrobatics check, one of the PC's leap onto the cart, gaining the +1 higher ground bonus. The bugbear responds by making an intimidation check against the remaining horse, accompanied by a swift swat on the rump. The cart lurches forward, and the PC on it keeps her feet with another successful acrobatics check. As the cart moves forward, the PC 'moves' through two of the bugbear's threatened squares...
Now the question: Does the bugbear get an attack of opportunity against the PC on the cart?
I gave him one. The party loved the combat, and when the bugbear was dead, there were handshakes and congratulations all around.
I may have made the combat more fun and memorable... but did I do the right thing?