And might as well update with something approaching a better write-up of that first idea.  It has been far too long since I've written a pitch for an RP.  Far, far too long.  Enjoy more information that's pretty setting-agnostic and possibly still too vague.  But hopefully it gives a better idea of how things work.  

From Beyond

You have entered into a sort of symbiosis with an extradimensional being.  You provide it with some of your magical energy and a way to access your world, and it provides you with the power to fight.  The world is not as small as you until recently thought it was, and worse, it’s under threat.  You’ve been tasked with saving it.  

If only it were that simple.  There’s a whole secret war going on, and while it means you can find help, it doesn’t make it any less daunting of a task.  Your allies: the Eldritch Society, a loose organization of sorcerers and occult scholars.  Armed with knowledge of the enemy, they fight their shadow war against occult threats.  And it was, after all, one of their rituals gone awry that got you into this in the first place…

So you’re bonded in symbiosis with an extradimensional creature.  What does that even get you?  Quite a lot, actually.  While some abilities will depend on your specific symbiont, many abilities are common to all.  

You can mentally call your symbiont at any time to form a sort of armor around you.  The transformation is near-instantaneous, and cannot be stopped by normal means, even destroying bonds or other things right next to you.  Your new form is clearly monstrous, but also quite powerful.  The specific appearance and attacks depend on the type of symbiont, of course.  You've even got a sort of really powerful attack you can only use once a day, whether it be a giant anime wave motion gun or teleporting around and hitting everyone in the room or whatever else.  

When transformed, your physical abilities are greatly enhanced, and you regenerate from injury quickly.  Even when not transformed, you have lesser improvements to your abilities and still heal quickly.  Note however that your symbiont won’t let you drop your transformation until any injuries are healed, and any injuries taken in human form will heal at the rate for your human form, regardless of which form you are in. Most importantly, perhaps, you can sense monsters.  Anything inhuman, you can now pick out with a sort of sixth sense, although it can take a bit of study to really be sure.  

Shadows in the Dark

Your primary enemies are the Children of Chaos, a cult that has infiltrated a powerful corporation, and now controls it from the inside.  Careful to operate in secret, they carry out their work for Nyarlathotep subtly, while the public face of the corporation remains unchanged.  Their most dangerous agents are the dhoanoids, monsters who can take the form of men.  A dark mirror of your own powers, these creatures may be able to appear in their human form, but the ritual that creates them leaves nothing truly human behind.  

You know about magic.  It’s something you can learn in school if you have the gift for it.  Of course, sorcerers are expected to register with the government and are carefully monitored, unless they go underground.  Among those that do, some take a darker path, often even giving up some aspect of their humanity for greater power.  Unlike dhoanoids, who can learn and use magic if they choose, sorcerers pursuing such paths to power are often strange and varied in their methods and abilities.