A malignant evil lurks in the deep black depths of the ocean. In the sunless trenches and vast sea caverns an ancient power waits and plots.
To help with the task of directing Crabmen forces and other lesser creatures the Deep Masters decided to create a class of leader creatures.
These leader creatures are often created using humans which are recovered during Crabmen raids, which are then spliced with various sea dwelling creatures. The resulting abominations are horrific mockeries of the humanoid form which sprout tentacles, claws, scales, gills, fins and bulging eyes in truly unsettling combinations. Each of these creatures are unique and shares a deep telepathic bond with the Deep Master who created them.
These leader creatures are far less suitable for combat then the Crabmen but will often supervise them on their raids. These agents travel far abroad to further the interests of their Deep Master overlords, using powerful but subtle magic to blend in and influence events in the surface world.
-The big reveal about who the Deep Masters are is coming in part 3.
(It's not really that big a secret though, I bet most people could guess it.)
And yes this is how Mindflayers work in my campaign world, they have a heavy nautical theme and I've dropped the whole alien brain stealing thing.