How about an "oversight" of beholders?
Also, here are a bunch that came to me while perusing Monsters of the Multiverse
A "suck" of stirges
A "flutter" of faeries
A "hoppening" of harengons
An "amazement" of minotaurs
A "misery" of meazels
A "torment" of meenlocks
A "mimicry" of leucrotta
A "corruption" of nagpa
An "overmind" of neogi
A "crush" of ogres
A "quickening" of quicklings
A "bloodbath" of redcaps
A "gloaming" of shadow mastiffs
A "suffering" of sorrowsworn
