This version of the beholder Cause Serious Wounds Ray is only released by Hive Mothers and Death Tyrants.
It is more destructive than the typical Cause Serious Wounds Ray of other Beholders and is released by the two aforementioned beholder subraces with zero cast time. In general, all types of beholders don't really have to "cast" their eye ray attacks, since it's really a released ray of magical energy, and the eye ray cannot be interrupted with a successful hit.
Gameplay[]
The creature selects a single enemy creature that is in range and then releases a ray which speeds unerringly to strike the targeted creature, inflicting 5d8 points of Magical damage. The eye ray is derived from the aberration's internal magical energy and therefore can't be prevented by Miscast Magic effects, Silence or spell casting interruptions (such as damage).
This ray bypasses Magic resistance, but a Spell immunity: Necromancy will negate it completely.
Since this eye ray is considered a level 4 spell effect it can be blocked by any Spell protections type defense with enough protective capacity - for example, a Minor Spell Deflection or Globe of Invulnerability. Likewise, a Minor Spell Turning, Spell Turning, or the Shield of Balduran will reflect the eye ray back at the beholder. However, a Minor Globe of Invulnerability can't block this ray.
As this eye ray is classified with a secondary type offensive damage spell, the Cloak of Mirroring will deflect it.