Thaxalia was a beholder that the Red Wizards summoned and bound with the secret complex of Doomvault under Thaymount. It was maimed of its central eye and death ray and disintegrate eyestalks so that it could not attack its Red Wizard masters.
In 1486 DR, when the heroes of Daggerford encountered it, Thaxalia could suggest an alliance against the Red Wizards. Thaxalia could be convinced to help the adventurers but breaking the curse that bound it was not easy. As it was an aberration and an evil monster, there was little hope of a true alliance with it, more of a mutual exploitation.