What is the cmD of Forceful Hand when someone pushes against it to get to the caster? Assume the caster can use his caster level in place of BAB for cmD, and the hand's DEX is 10 ... which results in a cmD = cmB?
This spell functions as interposing hand, except that it can also pursue and bull rush one opponent you select. The forceful hand gets one bull rush attack per round. This attack does not provoke an attack of opportunity. Its CMB for bull rush checks uses your caster level in place of its base attack bonus, with a +8 bonus for its Strength score (27), and a +1 bonus for being Large. The hand always moves with the opponent to push them back as far as possible. It has no movement limit for this purpose. Directing the spell to a new target is a move action. Forceful hand prevents the opponent from moving closer to you without first succeeding on a bull rush attack, moving both the forceful hand and the target closer to you. The forceful hand can instead be directed to interpose itself, as interposing hand does.
I suspect that's a non-issue, as the hand operates just like Interposing Hand, so you can't get past it, but big creatures can push it back at half speed. It still provides Cover, even at melee range.
So it might go as an alternating exchange of pushing one way, then the other, each on its turn. If that sounds silly, just combine the overall result into one move.
Forceful hand prevents the opponent from moving closer to you without first succeeding on a bull rush attack, moving both the forceful hand and the target closer to you.
You need to make a Bull rush check. The CMD is needed.
The text of the spell is more or less that of the 3.5 version, so probably someone forgot to update it correctly and no one noticed or take the time for an update.
The Hand has a BAB (the caster level of the caster), a Strength score (27), and a size (large). A Dexterity score is not mentioned, so we can assume that it has a Dexterity or 10 or -. Both give a modifier of 0.
So we can calculate the CMD:
If you look at crushing hand. . .
This spell functions as interposing hand, except that it can also grapple one opponent as grasping hand. Its CMB and CMD for grapple checks use your caster level in place of its base attack bonus, with a +12 bonus for its Strength score (35) and a +1 bonus for being Large (its Dexterity is 10, granting no bonus to the CMD). A crushing hand deals 2d6+12 points of damage on each successful grapple check against an opponent. The crushing hand can instead be directed to bull rush a target (as forceful hand), using the same bonuses outlined above, or it can be directed to interpose itself, as interposing hand does.
Looking at a few other spells like black tentacles or incorporeal chains as well, it seems that the default CMD for spells that use maneuvers is CMB + 10. (Which is the same difference as a creature with no Dex modifier.)
So Diego your take is that it uses caster level in place of the caster's bab to make a bull rush attempt, but it uses the caster's bab when it is being bull rushed? So it pushes harder than it resists being pushed?
No, I repeat:The Hand has a BAB (the caster level of the caster),
The BAB of the hand is set when the spell is cast.