Campaign Conundrum 3 - Bull Rushing

[reveal]

What I'd do is let him enter the square of his target, provoking AoOs as normal, and then determine whether or not he's got a valid target.

If the target's a mirror image, it pops. The bull-rusher may elect to continue along his line of advance, up to his normal movement (if a move / standard combination) or up to double his movement (if a charging bull rush).

If the target's real, resolve as normal.

I agree. I think this is a case where realism actually should be implemented because it's easy to imagine. It's like in American football where a guy tries to tackle another guy. If the guy ducks out of the way, the tackler doesn't just stop and jump back because he's grabbing air; he continues to go forward because his momentum is carrying him that way.

 

[VorpalStare]

What's wrong with using the equivalent rules for an Overrun attack when the target avoids the attack?

From Overrun, p. 157 PHB:

Step 2: Opponent Avoids?
The defender has the option to simply avoid you. If he avoids you, he doesn't suffer any ill effect. If you were attempting the overrun as part of a charge, you may keep moving. (You can always move through a square occupied by someone who lets you by.) In either case, the overrun attempt doesn't count against your actions this round (except for any movement required to enter the opponent's square.) If your opponent doesn't avoid you, move to Step 3.

Substitute "bull rush" for "overrun", and use the option for the target avoiding the "bull rusher".

This has precedence in the rules and makes sense.