Some players have wondered why Stalkers of the Elder Dark features only three of the Opherian Mysteries. There has to be more, but we hoped to avoid even a level playing field with the cosmic horrors characters will inevitably face. That said, there are other dreadful Mysteries to be uncovered (and used) in a Faustian bargain, for no power comes without its price. So being October, a month of horrors, here's a fresh offering...
BODIES CHANGE transforms the caster into an abaloth, with all the physical attibutes of one while retaining their human faculties. This utterance deals an instant 2d6 trauma, with 1d6 additional points per day spent in this condition. Traumatized characters ignore their phobias in this state; but mental breakdown causes them to become true (and mindless) abaloths pending recitation of an Elder Sign in the presence of the affected individual.
The above can be used to survive the void of space and/or withstand the debilitating effects of one's greatest fears, noting that phobias become active again upon resumption of the character's human form and faculties. Of what use this was to the Opherians remains lost to deepest time, although some writings suggest a reproductive process, if not a gift to cults consecrated to The Elder Ones. It may be best not to know such secrets...
Once again, fair fights are antithetical to cosmic horror. That doesn't mean the players have no chance against the darkness. Far from it. But it does mean the characters are at best unnerved; and when taking up the tools of the enemy, they do so at tremendous personal risk as befits the terrifying powers at work. And if your players know even a hint of real fear at risking a beloved character's humanity, Stalker's true purpose has been realized.