What follows is an approximation based on my holistic grasp of monster design in the 13th Age core book; suggestions/tweaks welcome!
Hyshkorrid: The Mind Flayers of Lingusia in 13th Age
Lingusia’s breed of mind flayers are creatures from beyond the stars that crash-landed on the world long ago, their ether engines rendered inert at a time when such devices could not function in the atmosphere of the world. The unique restrictions which prevented the function of ether engines disappeared after the god Etah began his cosmic pilgrimage centuries earlier, but by then the stranded mind flayers had imbedded themselves into the hideous cultures and politics of the Underworld.
Hyshkorrid are known for their obsession with mentally enslaving and feasting on the brains of other species; all other species are lesser species in their minds.
6th Level Caster
Mind Blast +10 vs. MD against 1D4 nearby targets; 16 psychic damage and target is stunned. Each round the target can make a Save (11+) to recover from the stun. Attack roll 16+: one target is also dominated. Attack roll natural 20: the mind flayer dominates all targets.
[Special Effect] Domination: this effect lasts until the target makes a save (11+); each round the mind flayer may direct one action of the target (either a move, standard or quick). If the target rolls a 1 on the save the mind flayer may direct two actions instead.
Tentacle maw melee attack; +11 vs. AC; 12 damage and target must make a save (11+) or take an additional 12 psychic damage. This attack is automatic against adjacent helpless/stunned targets.
[Special Trigger] Brain Extraction: +10 vs. PD; damage as follows (special) target must be engaged with the hyshkorrid and helpless/stunned with 0 HPs; as a swift action the hyshkorrid attempts to devour the brain. The victim who fails a Save (11+) has his/her brain extracted. The hyshkorrid gains 10 temporary hit points and the victim dies. If the save succeeds the victim takes 1D6 damage.
Nastier Specials: Dominator
The dominating mind flayer specializes in mind controlling thralls. In place of the Mind Blast the mind flayer can attempt to dominate rather than stun. Any target that becomes subject to its domination effect and fails three saves in a row is totally dominated for the remainder of the day (all actions determined by the mind flayer) and makes a new Save (11+) once per day thereafter. If the thrall fails three daily saves in a row then the saves changes to once per week.
MD: 19 HP: 72