As described in this very informative post
on SHS.Quotes from the post:
Attack animations can be adjusted by tweaking values in abilities of weapon ITMs. These are:Overhand swing:
[%] (SLASH animation/sound effect)Backhand swing:
[%] (BACKSLASH animation/sound effect)Thrust:
[%] (JAB animation/sound effect)
The values are percentages; they represent the chance for each animation to be played along with the sound effect assigned to it in the 2DA soundset.
If a monster is wielding a weapon with disabled animations, it won't use the frames and sound effects that had been previously designed specifically for it.
Take a look at the Dancing Sword animation (Code: MDSW; e.g., Ras or Spectral Blade). It has frames for slashes, backslashes and jabs. [...] Now look inside SWORD02.cre (Ras) and SWORD68.cre (Spectral Blade). They both use weapon ITMs with disabled JAB animations. The player never gets to see the JAB animation or hear it's accompanying attack sound effect.
And unfortunately, there are quite a few creatures suffering from the exact same issue. It's typically because the devs re-used exisiting item templates or assigned generic weapons to special-case creatures. For example, Githyanki wield two handed swords in one hand. The Githyanki animation (MGIT) has all the attack frames (SLASH, BACKSLASH and JAB), but the majority of CREs using the animation have generic Bastard or Two Handed swords assigned to primary weapons. These weapon ITMs are usually 50% SLASH and 50% BACKSLASH -- again, no JAB animation/sound effect.Note that this affects BG:EE, SoD, and BGII:EE in equal measure and spans across almost all CRE/ITM files.
Beamdog ticket BGCS-3405.@Galactygon