DnD 4E Rules I Don’t Like [III]: Combat Advantage doesn’t stack
Page 280 of the PHB lists 15 different ways to gain combat advantage — and there are more. But there is no advantage to stacking these unfavorable conditions which makes the game a bit easier, but really doesn’t make any sense:
Senario 1: You are attacking a troll. The troll is unaware of you so you have Combat advantage — +2 to your attack roll.
Senario 2: You are going to attack a troll. Two of your companions have flanked the troll, and the troll is dazed from an attack by your warlock companion. You have remained hidden so the troll is unaware of you. You have combat advantage 2 ways (dazed, unaware), or 3 ways in my reckoning (flanked, dazed, unaware), but your bonus to your attack roll is still +2.
When fighting stronger opponents it is very helpful to be able to stack as many tactical advantages as possible to increase your chances of hitting and doing damage — in other words wolf pack tactics. But it doesn’t make sense to stack some of the conditions (like Surprised and Stunned). My rule:
Combat Advantage (Mental): The defender’s mental condition has been compromised such that it is less able to defend itself. The attacker gains a +2 Mental Combat Advantage bonus to attack if the defender is Dazed, Helpless, Stunned, Surprised, or Unconscious.
Combat Advantage (Physical): The defender’s physical situation limits its ability to defend itself. The attacker gains a +2 Physical Combat Advantage bonus to attack if the defender is Balancing, Climbing, Prone (melee only), Restrained, Running, Squeezing.
Combat Advantage (Tactical): The attacker (or his allies) has the defender in a advantageous tactical situation. The attacker gains a +2 Tactical Combat Advantage to attack if the defender is Flanked, Unable to see the attacker, or Unaware of the attacker.
Stacking: Combat Advantage bonuses do not stack within type, but an attacker can stack Combat Advantages of multiple types. For example, an attacker would have a +6 bonus against an unconscious opponent with a melee attack (Mental: Unconscious, Helpless; Physical: Prone; Tactical: Unaware of, Unable to see attacker).
This is more complicated but strongly rewards parties (and nasty DMs) when they think creatively to place and opponent in the worst possible situation.