His power is proportional to his control over you, and the reverse is also true.

Now that's what I call a demonic bargain! So what you're positing is that this imp, once linked to you, will lend you power corresponding to your level of influence over him... But if he should be the one gaining 'influence' over you, then his personal power will grow instead?

I'm sure you know what you're doing, and have already considered the... Precarious relationship you'll be entering into. If, when push comes to shove, it turns out that you do have the will to dominate this toy-sized tease, you'll reap the magical benefits that will bring (and, I should expect, you'll be able to test out at least some of those powers on your new plaything).

However, if you lack the strength to command the respect of your impish stud, and feed a pattern of subordination and appeasement instead, you'll be lowering your defences and opening the door for all sorts of magical misfortune, in the form of sadistic reprisals by your tiny and untrammelled tyrant.

Are you sure you agree to these conditions?