Beholder in a 3rd-level party - what's the worst that could happen?

[AvatarVecna]

Are we talking 3.5? Because if so, you need to ban Beholder Mage or watch as the game completely falls apart. If the player specifically asked to play a Beholder in a low-level game, there's a good chance they're aiming for Beholder Mage, although it's hardly a guarantee (some people like weird character concepts); if the player was offered a Gauth (Lesser Beholder) and rejected it for not being a "real Beholder", you are virtually guaranteed to have a Beholder Mage on your team soon; if the player's backstory or initial acts in-game involve gouging out the Beholder's central eye, please tell them that Beholder Mage is banned in your game (if it's a backstory thing, they likely told you it's because they don't want to be overpowered with an antimagic eye, but this is in all likelyhood a complete fabrication).

EDIT: I'm only asking whether it's 3.5 or PF because the OP mentions PF in a tangential way, and there's no PF tag. Needless to say, the above can be ignored if this is about Pathfinder Beholders, which don't have quite the same broken BS available that 3.5 had.