For the Abilities, there is no limit on how much you can do this, where, or when.
For the limitations, they cannot be avoided in any way. If you cannot do something, you will never be able to.
1. If the human partner allows, the inhuman individual may change forms freely.
Inhuman characters can freely switch between their forms, or even adapt traits of one form when in the other. (Ex. Human appearance, but willing themselves to grow horns from their true form, or their eyes changing into the eyes of the other form.)
2. Inhuman Individuals cannot kill their human partners.
Inhuman individuals cannot, under any circumstance, kill their partners. If an individual is to try, an unseen force shall keep them from doing so and inflict upon them a moderate level of pain for several seconds.
3. The human partner can summon their Inhuman partner at will.
A human can summon their partner at any time and place.
4. A human partner gains some of their Inhuman partner's abilities and may use them freely as their own.
When entering a contract, a human gains an ability of the species their partner is. this ability can be used at any time on anyone, now completely for the use of the human. (ex. A human with a succubus partner can seduce others, A human with a vampire partner becomes faster or stronger.)
5. A human may disable the abilities of their inhuman partner at any time.
A human partner can keep their inhuman partner's abilities on lockdown, making their inhuman partner unable to use their race's powers. They can even specify a specific power that cannot use. HOWEVER, THIS ONLY WORKS WHILE THE HUMAN PARTNER IS AWAKE.
6. While in human form, Inhuman partners will be vulnerable to harm in any way a human would be.
While in their human form, Inhumans can sustain damage like any human - Although they heal at an accelerated pace (if their race does, at least) and they can take much more damage (Durability far exceeding that of normal humans).
7. Partners will develop and keep and telepathic link.
Parts may communicate back and forth through a telepathic link, speaking to one another through their minds. However, they cannot communicate if spread too far apart, and both parties must be conscious.
More Abilities and Limitations may be added or edited. Please check frequently. All RPers will be notified if there are any additions to the list. Suggestions are welcome, but may not be accepted.