Well, this one's just kinda goofy, but I do it a lot.

Quack Suicide SQUAD!

When I've successfully made my crusade against Jerusalem/Acre, the Mongols ALWAYS come for me...

So, I've got my Anti-mongol tactic, which the AI ALWAYS falls for.

Usually the AI's pretty good about sitting outside the range of my ballista turrets/cannon turrets. This is when the Quack suicide squad comes into play.

Works best with a cheapo unit with shields. Open the gate sit a unit right outside it. Without fail, up charge the mongol horse archers, to kill the ONE unit sitting outside the walls.

Cue "Quack Suicide Squad, ATTACK!"

Until the unit dies, to the LAST MAN, or routs, the ai will continue to sit in range of every piece of ranged weaponry I've got, taking hideous casualties. (Maybe they suggested something about their mother?)