If you interrupt a foe activating a skill that is easily interruptible or the target is dazed, you will not deal bonus damage.
Heroes in avatar form are comparatively smaller than humans.
All Avatars can be recharged with Eternal Aura (though not kept up indefinitely at 0 Mysticism since the duration change).
Consider bringing an IAS like Heart of Fury, to have a better chance of hitting an enemy activating skills.
Consider bringing along Radiant Scythe. You will almost always get the max damage.
Bug! When this avatar form ends, your character may be temporarily invisible until moving to a new location. This may be true of all avatars. Gameplay is not adversely affected.
According to the Nightfall Manuscripts, the form that the player takes on while in the Avatar of Lyssa is of the Elonian image of the god, using masks to show many faces of beauty, instead of twin sisters.