Shoggoth - Retail Only

It was a terrible, indescribable thing vaster than any subway train—a shapeless congeries of protoplasmic bubbles, faintly self-luminous, and with myriads of temporary eyes forming and un-forming as pustules of greenish light all over the tunnel-filling front that bore down upon us, crushing the frantic penguins and slithering over the glistening floor that it and its kind had swept so evilly free of all litter.

— H. P. Lovecraft, At the Mountains of Madness

Shoggoths are extremely hard to kill and will be tough opposition for any Agents.

You can find rules for the Shoggoth here