- Trade defense for offense (in terms of one of accuracy, movement, or power)
- Trade offense for defense (in terms of number of defenses or effectiveness of defenses)
- Trade time not-attacking for some sort of aiming bonus to your next attack against a specific opponent
- Set up If-Then statements, like "I wait until he tries to attack me to launch my attack against him". This would let you delay your own action in the initiative sequence in exchange for potentially interrupting another person's action with your own.
- Move further than you normally could if you also attacked
- Move far AND attack, but with penalties to accuracy and defenses
- Do Jack Squat.
- Take a round to execute a non-combat action during combat
- For the sake of spellcasting, probably some sort of Concentration thingy instead of an attack, with potential penalties or different handling of defenses (or the effect of distraction, at the least).
I think a trick system should be able to let you take various penalties to skills to perform tricks. Frex, roll Acrobatics-4 to slide down a banister without falling off. Buying up a trick should eliminate the penalty. It is totally okay if it is cheaper to buy up the underlying skill than buy up every trick based on it; people tend to specialize in tricks anyway. It's sort of a signature thing.
Executing tricks should take various numbers of rounds based on the trick. Performing a backflip might be a one-round action, but sliding down a bannister will take various lengths of time depending on how long that bannister is. This will generally use the Non-Combat-Stuff maneuver above.
Combat tricks may involve exploiting the geometry of your weapon (using the hook on locherbe axe to snag someone's clothing or using the prongs on a spontoon to bind an opponent's blade). These will likely use some form of an attack maneuver.