It expects adventurers to contract Vampirism and use Gaseous Form to creep in through the cracks before using scrolls of True Resurrection obtained from a Ki-Rin to regain life. Like it expects adventurers to kick in the door. Namely, instead of just being paranoid and expecting attack, a Beholder literally thinks of every single possibility in existence and plans against them.
For the first time I'm reading through the Beholder section, and I see that their famous paranoia has been refluffed a little for 5e. So I love Volo's Guide for the contextual fluff it adds to monsters, especially fire-and-forget monsters that previously missed out on a lot of complexity like Giants or Hags.
