On the subject of Pokemon AI, it occasionally has major problems trying to deal with abilities that lend immunity to damage, especially the less common ones. Although it's always aware of Levitate, the AI on PBR seems quite happy to try and defeat my Electivire with Electric-type attacks, which do no damage and merely increase my Speed stat thanks to Motor Drive. Shedinja's Wonder Guard often creates a lot of comedy as well, with one example being in the Battle Factory where an opposing Clamperl attempted to use Water Pulse to defeat Shedinja, to no avail, before eventually finding the sense to use Toxic to get around Wonder Guard and KO Sheddy.
Brawl's had some rather stupid AI issues as well, which is surprising given Melee's (usually) impressive Lv.9 AI that was actually capable of chaining together moves into combos frequently enough for you to know that it knew full well what it was doing. Brawl's Lv.9s though are sadly disappointing - their only real claim to fame is their superhuman reaction speed, being able to instantly move on the very first frame of recovery from an attack. Otherwise, if it isn't Meta Knight getting edge-hogged for trying to use Dimensional Cape as a recovery move (MK getting edge-hogged should NEVER happen) or Snake blowing himself up with his own grenades and mines, then the AI is most likely off-stage letting itself get edge-guarded to hell and back, successfully turning all but the most amazing of recoveries (Dedede, MK, R.O.B. and Pit basically) into completely useless moves that may as well not exist. Another indication that the creators of Brawl spent too much time cramming as much as they could into the game and not enough time making sure the game itself was actually good...
Other than that, most of the enemy AI in games tends to be quite good. Now all we need to do is give Dom from Gears of War some chainsaw bayonet-style brain surgery and we're good to go...