Reddit mentions of Wheater's Functional Histology: A Text and Colour Atlas (FUNCTIONAL HISTOLOGY (WHEATER'S))

The one I'd probably want: chemical manipulation. Stick your finger in a glass of apple juice and make cider. Slap someone you hate and give them third-degree burns.

Limitation: you can only cause a specific reaction if you know how it works. THIS IS YOUR LIFE NOW.

Other ideas:

• "Invisibility" through warping light (i.e. active camouflage), but at the cost of being able to see anything. If the light passes around you, it can't enter your eyes.
  
• The ability to control objects' speed or momentum, but only as long as you're touching them (you can slow down projectiles, but you'd better have hella good reaction times).
  
• Healing/regeneration, but with the same caveat as above. And the same outcome.
  
• Aura transfer, for purposes of both healing and murdering. If your own Aura gets depleted, though, you automatically leech it from anyone you touch.