Earlier this year, Rafael Chandler shepherded #Narcosa to life -- a collaborative, psychedelic OSR megacompendium available for free. (You can download it right now, if you don't already have it.)
Now, he's rallying the G+ gaming community (and beyond) to create #Narcosmos, a collaborative, psychedelic megacompendium IN SPACE. Obviously, I can't NOT participate.
My contributions will be easily adaptable to your favorite Old School RPG, and these could be considered Crawljammer bonus features. The stuff that the Crawljammer overlords don't officially want you to see, because Crawljammer is printed in black and white, and these ideas are in mind-altering technicolor (as my first entry will demonstrate)!
So, here we go...launching Narcosmos...
The Tiger-Soul Rainbow Quintessence
In your travels through the psychosphere, you may encounter the Tiger-Soul Rainbow Quintessence in one of two ways: (1) it stalks you from the edges of your consciousness as you fly through the void of space or teleport to a distant world, then pounces and devours you hours later, or (2) you slowly, terrifyingly begin to realize that you have been trapped inside the creature for weeks, and it has already begun feeding off your psychic energy. In the latter case, you must escape or transform. There is no alternative.
A psychic amalgam of lost souls and desperation, the Tiger-Soul Rainbow Quintessence appears in its primary form as a hint of light at the edges of your eyes, then when you are alone -- the first around a corner, the last in a room -- it strikes. Horrifyingly, gorgeously vibrant in its hues of pink and green and purple, throbbing with the majesty of prismatic mind-energy, the great cat-shaped creature bares its blurred teeth and lunges at the core of your being.
Tiger-Soul Rainbow Quintessence (Animal Form): AC 2 (17); MV 50'; HD 7; #AT 3: claw/claw/bite (1d8/1d8/1d12). On a successful bite attack, save vs. death or the Tiger-Soul deals 1d6 damage to your Intelligence and Constitution and instantly transports you back to its lair -- a small black hole in the psychosphere.
Your adventuring companions may follow the trail to the beast's lair to recover your body through astral projection or planar travel or spirit walking via shamanistic means, but unless you are prepared to confront the Tiger-Soul Rainbow Quintessence on your own, you should think twice before journeying across time and space.
The secondary, and more terrifying, aspect of the Tiger-Soul is in its abstracted form. To a visionary or a seer, its abstracted form would look like a 30' tall translucent, rainbow-hued tiger, surrounding its victim like a ghostly shell, mimicking its every move, leeching energy with every step. To the victim, and to anyone without a psychic connection to the spirit world, the creature is intangible and invisible. You only become aware of it in your dreams, after 1d4 weeks of living inside the creatures unreal aura, and when your consciousness fully accepts that you have become inextricably linked to this extradimensional creature, you cannot escape. Only a banish spell or the equivalent will send the beast away and detach your psychic umbilicus. Otherwise, you will lose 1d4 hit points per day after the moment of realization occurs...until you die, and then your departing consciousness will transform into the animal aspect of the Tiger-Soul Rainbow Quintessence yourself, first lurking in the shadows of the psychosphere, seeking a lair in which to rest, then hunting your own prey across the reaches of spacetime, then, after 100 years, growing larger and more abstract until there is nothing left but to continue the cycle anew.
Tiger-Soul Rainbow Quintessence (Abstract Form): AC -2 (21); MV 100'; HD 15; #AT 1: bite (1d20). The Abstract form of the Tiger-Soul is invisible and intangible, and can only be damaged by psychic energy and soul-bound weapons. A Tiger-Soul linked to a victim will drain 1d4 hit points per day and add those hit points to her own total. Only a banish spell (or its equivalent) will dissolve the connection with its victim, sending the great beast away, but a system shock check is needed or the victim will immediately die after being disconnected from the Tiger-Soul Rainbow Quintessence.