If you're the one to light a candle, it will never burn down, nor will any sudden gust douse the flame. It may still be snuffed, however.

You have the power of a perilous exchange; by granting another a modicum of mastery over yourself, you can -every time they control you- take some of their life-force, healing your own ills and staving off the debilitations of old age.

you have the power to use plants to steal the life force of other to make yourself immortal

You are an ancient ghost with the power to possess others; melding their life with yours and stealing their knowledge and memories to become a sort of super-gestalt, endlessly accumulating more lives -and more insanity.

You can freeze anything to absolute zero!

You have a superpower of bargaining/haggling; you can tell exactly how far the other party is willing to go and thus always get the best deal possible.

You can change someone's vision so they can see in only black and white. It's possible for you to turn their vision back, too.

You need only be exposed to poetry in any given language to gain an intuitive understanding of it. However, unless you immerse yourself in said language for a minimum of a fortnight, you can only express yourself in poetry.

Hrm... I'd say your power is at its strongest during a full moon, but even then, you have the strength and ability to erase the darkness that dwells in a person's dreams with a serene, almost eerie calmness.