So, I have a guy in my campaign who has a halfling wiz. He shrinks himself down to tiny and then rides his familiar around like a mount. Question is. If the familiar (with halfling aboard) flies thru a threatened space can the monster get an attack of opportunity against the character? Of course he can against the mount but if combat reflexes ... can the monster attack both? Rules are vague on this. As the mount is using the "move action" and not the character.
