The Necronomicon.
No, how about this.
A jet black (to contrast with my pasty white skin) tribal-style tattoo that covers my entire body. It hovers just slightly off the surface of my skin because it's some kind of eldritch biological magic/science developed by unspeakable aliens from the black spaces between the stars who are naught but tangible gases of hideous colour.
Now, this 'tattoo', which is actually a mindless, harmless symbiotic entity, can be utilized for all sorts of things. Not only is it a conduit to the vast collective intelligence of the gas creatures, it can be reshaped into wings, tentacles, claws, a shield, armour - you name it. It also acts an extra organ to help breathe in outer space or under water, reshaping my very biology to adapt to my suuroundings or situation.
Also, due to the eldritch nature of the gas creatures and the symbiote thing, it can not only peer into certain outisde dimensions, it can for a prolonged period, travel through them, but the human host stops indefinite exposure to outside influences.
There's an ethereal quality to it, and it looks faded in bright light, but never completely vanishes.
I would name it:
The Lotus Configuration
Sort of like Alex Mercer, but spooky and Lovecraftian and in no way like Alex Mercer whatsoever, really.
I did that all with no forethought...just typed it...I have too much time on my hands.
And the Necronomicon. Maybe