What happens when the space behind someone is already occupied by a wall? Do they take damage, fall prone, does it not work etc.?
[RPG] Bull rushing into a wall
dnd-3.5e
Related Solutions
As a matter of fact, Spider Climb does not allow to traverse frictionless surface automatically, much as the spiders can't traverse glass, for example. All it does is granting climb speed to its subject, and that doesn't even mean automatic climb success:
A creature with a climb speed has a +8 racial bonus on all Climb checks. The creature must make a Climb check to climb any wall or slope with a DC higher than 0, but it always can choose to take 10, even if rushed or threatened while climbing. If a creature with a climb speed chooses an accelerated climb (see above), it moves at double its climb speed (or at its land speed, whichever is slower) and makes a single Climb check at a -5 penalty. Such a creature retains its Dexterity bonus to Armor Class (if any) while climbing, and opponents get no special bonus to their attacks against it. It cannot, however, use the run action while climbing.
Still, climb skill could be used to traverse horizontal surface
With a successful Climb check, you can advance up, down, or across a slope, a wall, or some other steep incline (or even a ceiling with handholds) at one-quarter your normal speed. A slope is considered to be any incline at an angle measuring less than 60 degrees; a wall is any incline at an angle measuring 60 degrees or more.
but in the case of "magically frictionless" surface skill check will either receive penalties (-5 for slippery surfaces, I'd suggest at least -10 in the magical case) or be outright impossible (if it is also perfectly smooth).
Note: creatures with climb speed moves at its full climb speed while climbing, or at double that (but not greater than its base land speed) while performing accelerated climb.
The spell seems to be written with the idea that the huge creature would take "waves of heat" damage on the caster's turn if the creature were in range of the "waves", and "passing through" damage on the creature's turn if they moved through the wall of fire. By a simple reading, the creature would take the "waves of heat" on your turn, and "passing through damage" on the creature's turn. The same would repeat the following round if the creature was still occupying space in both the "waves" range on the caster's turn and "passing through" range on the creature's turn.
This post is similar, though dealing with a different issue.
After re-reading the spell description, it does appear the creature takes "passing through" damage on your turn (because it's "if you evoke"). With that in mind, I think the first round, the creature would take "passing through" damage on the caster's turn, and then on their turn, if they don't (or can't) get out, "passing through" again. On subsequent rounds, I would treat is as above.
Best Answer
Usual Rule
It counts as a successful Bull Rush for the purposes of any abilities that care about things like that, but they do not move.
Shock Trooper
This feat from Complete Warrior, most famous for its ability to allow you to apply Power Attack penalties to your AC instead of Attack during a charge, also allows you to move foes that you Bull Rush to the side, as well as forward. So if they’re against a wall, this could allow you to move them along the wall.
It also allows you to Bull Rush one enemy into another, knocking both Prone.
Dungeoncrasher
The Dungeoncrasher ACF from Dungeonscape allows a Fighter to do sizeable damage (8d6+3×Str) with this maneuver. This is so reliable and potent that this ACF alone is enough to push the Fighter up a Tier.