My lord, the games AI is awful. If there is something blocking the fire path between the ai and you it sits there and does nothing every turn. You are forced to get into an easy shootable range for them just to make it go faster.
If you want all achievements, get the "Fly less then 10 feet" one first, DO NOT PURCHASE ANY EXPLODING STUNS UNTIL YOU GET THAT ONE OR IT WILL BE IMPOSSIBLE TO GET!