Dark Young (1988)

Notes:

Sandy Petersen worked on Quake and some of the Lovecraftian monsters were based on the designs from 1988's "S. Petersen's Field Guide to Cthulhu Monsters: A Field Observer's Handbook of Preternatural Entities": the spawn is literally right on the cover.
While Shub-Niggurath herself does appear in the book the design used in Quake is basically an immobile version of the Dark Young (which are Shub-Niggurath's offspring).