Knockback Questions

[Hanuman]

I'm not super versed in the entire concept, is there a standard system this draws from other than bullrush?
If a foe is in your square can you knock them back in any direction, even up or down?

[Oddman80]

If you score a hit while you are using the Power Attack feat, you can make a free bull rush attempt against the foe you hit, applying the number by which you reduced your attack roll as a bonus on the opposed Strength check (as well as on the damage you deal). If you hit with a two handed weapon, you can apply double that number on the opposed Strength check. Unlike standard bull rush attempts, knockback attempts don't provoke attacks of opportunity, and you don't move with the enemy you knock backward. Bull rush rules can be found on page 154 of the Player's Handbook.

You aren't actually bull rushing the enemy. You don't actually move into their square (hence no attack of opportunity). You are hitting an enemy so hard with your melee attack, that you are knocking them backwards. The opposed strength checks typical of a bull rush are what is used as a mechanic to see if the opponent can resist the powerful blow's knockback

As far as direction goes, it must be along the horizontal plane, and along the path of a straight line. Additionally, each square the target is knocked back along that line's path must be further away from you than the previous square. As such, you may not knock the target sideways (the first square of movement wouldn't be any further away from you.

The easiest way to see the cone of allowable knockback trajectories would be in the players handbook illustrations of things with a cone shaped area of effect.

[Rebel7284]

If they are in your square, than any direction would be away from you.

[Hanuman]

Except for up or down, of course.

Thanks I may have to use throwing mechanics instead but the note about how the line of squares follows is interesting as if it is into the air it could possible arch or against a very buoyant target in water it could arch down then up.

The reason I'm asking is because we are designing a class around the videogame Super Smash Bros. (https://www.youtube.com/watch?v=nrVknUV880A#t=15m30s)

[Oddman80]

Are you referring to a tiny or smaller creature? One that was able to freely enter your square? Or were you talking about the mechanics of a typical bull rush, where you enter the target's square? If the former, than Rebel's response is accurate. If the latter, that, as I mentioned in my previous post, would not be relevant to using knockback.

[Hanuman]

For any reason really, such as a knockback out of a grapple, which would be a throw.