*Picks up his stick of prodding and annoying-ness +5, +7 vs. powergamers or munchkins, +9 vs. powergamers and munchkins*
Nice little critter in the Rogue's Gallery TFO, however, there are a few

nitpicks I have.
-Prices missing under equipment, and to have the Skittish Ring you need to have Skittish Nerves approved.
-Featwise I can't find Greater Multiattack at all in Masters of the Wild or Savage Species, mind telling me where to find it? Sorry if I overlooked it.
-Quote under the Insectile Template in Savage Species, "Despite having six arms, insectile creatures gain no additional attacks."
-Feral can only be applied to humanoid or monstrous humanoid not aberration or giant...although I'm not sure about how types were changed in 3.5e exactly.
Other than that things look mostly fine, nice mechanics on the Master Spell, should fit in with your background, just watch out against people with Iron Body or similar protections...
Edit-Btw, I think unless they changed Rend, you only get 1 rend no matter how much you attack, as long as you attack twice on the same creature, I believe this is how it is with the Girallon, as well as the Multiweapon Rend feat in the ELH.