Gauth (lesser beholder) Encounter

[pbdr]

So, I'm planning an encounter that involves a 3-sided fight with some enemies and a couple Gauths (lesser beholders from MM).

They are similar to the beholders, but their central eye is 30-foot cone with a one round stunning effect. I like the beholders's anti-magic cone attack and would rather the Gauth's central eye was more in line with that.

My thought is to make it a 60-foot antimagic cone that suppresses continuing effects (buffs and items), but can be cast through with difficulty. Mechanically, this would be the same as imposing spell resistance of 16 or 21 (10 or 15 plus HD). The caster level check would be for the Gauth to cast into the field and anything in the field already to cast.

How does this sound?

[Fouredged Sword]

I would have it be a field of disruption requiring a concentration check to cast in.

[Venger]

what characters is your party playing and what level are they?

gauths aren't that difficult to kill if you're the same level as they are, but if you're planning it as a challenging encounter for a party 2-3 lvls behind its CR, they may have trouble, especially if they're playing low op characters

[rot42]

The Spectator on page 141 of Lords of Madness is a Beholderkin with a Spell Turning effect in the central eye. This could be tweaked to an appropriate CR (4 by default, so probably lower than you are looking for) if you want something a bit more RAW.

Sticking with your "cone of SR idea" (which sounds like more fun), I would go with 10+HD unless that lowers the ability into meaninglessness. Consider adding two to the difficulty if a player is trying to cast from within overlapping cones. You should probably offer your players a Spellcraft or Knowledge (Dungeoneering) check to understand the effect when they see or are exposed to it, especially if they have Assay Spell Resistance or similar.