One thing that really pisses me off is when the AI blatantly cheats, and operates under different rules than the player.
In HoMM 2 the AI player can enter the moat and attack on the same turn,
but the player can't. Or rather, the player
can if using Auto Combat. Normally I don't get too hung up on such matters, since I can usually win anway. But in a pitched battle on a "Hard" map on "Impossible" difficulty it can make a difference.
In the specific game that causes the current butthurt I'm leading a Knight army of Rangers, Champions and Veteran Swordsmen and Pikemen against a Sorceress town defended by Unicorns, Elves, Sprites, Greater Druids and Battle Dwarves.
First round I cast Shield on my Rangers, my Champions enter the moat, the infantry moves towards the moat and the Rangers kill the Sprites.
The next turn the castle wall is breached at three different places. The Champions are next to the middle breach that is blocked by the defender's stack of Battle Dwarves. So I attack the Dwarves with my Champions and turn on Auto-Combat, assuming that the Veteran Swordsmen will follow up on the Champions' attack and do an unretaliated attack on the Dwarves. But instead they move to the uppermost breach, which is the only place the dreaded Unicorns can reach them. In the moat they are sitting ducks, especially after being subject to two Disprupting Rays. And to make matters wors the Veteran Pikemen don't attack the Dwarves either, but move into the moat next to the lowest of the three breches.
Here the champions have just attacked the Battle Dwarves. The optimal tactic now is for the Swordsmen to attack the Dwarves, while the Pikemen enter the moat at the breach at the bottom, where they are out of reach of that nasty stack of Unicorns.
Instead this is what happens when turning on Auto:
The Swordsmen make themselves sitting ducks for the Unicorns, while the Pikemen don't support the Champions.
I hate it when things like this happens, as they sour my enthusiasm for the game in question.
But the weird thing is that Googling does not turn up any other mention of this bug where only AI units can move into the moat and attack on the same turn.