When casting GMW on a weapon animated by shelgarn's it has only +3 to damage, but no ab increase.
Does Magic Weapon add AB?
Have you tested the bonus AB is truly missing (checking from the combat log once the blade hits) or is the bonus AB simply not showing on the character sheet?
Yes. Doesn't apply to the combat log nor the character sheet.
I noticed this myself when I tried to use the spell, but contributed to the AB increase from my Casting level preventing it from applying.
The enhancement bonus is surely applying, but some of its effects are being overridden by a higher attack bonus already on the weapon.
Attack bonuses affecting a weapon do not stack, only the highest one takes priority. This includes all ab vs race or alignment and weapon enhancements. Respectively, also, the attack bonus is what determines the ability to pass Damage Reduction in nwn mechanics. +1 ab from anything passes through +1/* DR, and +2ab through +2/* DR. This how nwn engine handles the rules.
I'm still a bit confused, as normal magic weapon works perfectly fine on shelgarns.
So why wouldn't gmw?
Because GMW is a different spell and uses different scripts (note also that GMW has been modified so that +3 enhancement is granted at level 10).
Also: this (http://www.efupw.com/forums/forum/information/efu-mechanics/81477-efu-spell-changes?p=666627#post666627).
if you're level 6, the animated weapon already has +3 AB. AB bonuses are not cumulative, but rather the highest takes effect. Therefore the reason GMW provides +3 damage only is because the weapon already has +3 AB.
If anything, this situation shows that MW and GMW combined with Shelgarn's is bugged because they should only be providing damage bonus, not AB bonus.
It's really a waste of a GMW to use it on Shelgarn.
However, Shelgarn is a super awesome spell with the new changes. The only issue is that it remains a circle 1 spell, hence it cannot really scale at higher levels
How about adding an exception to GMW to combo with Shelgarn leading to a more powerful effect? Makes sense thematically, and given that it's a circle 3 spell, it would remedy the scaling issue faced by this spell at higher levels.
Fun mechanic, it would be.
Just add an if "target = Shelgarn_ID"
SF transmutation : Expeditious retreat, +1 magic damage/3 caster levels, +2 temps HP/caster level, for 1 round/level
GSF transmutation : Haste, +1 magic damage/3 caster levels, +2 temp HP/caster level, for 2 rounds/level
Just an example. Could even be made cooler if we made bonuses that depends on multiple types of Spell focus, similar to the way Shadow Conjuration works.