It's a joy just to breathe

 Due to his scrying eye, Mr. Teatime can do the following:

• See the invisible
• See in the dark
• Spot almost-invisible handholds and footholds
• Find purchase on thin air for just long enough to get to same
• Move so fast he leaves a blur
• Be precise enough with a knife to tickle someone through four layers of clothing

(Slightly) more mundanely, he frightens senior Assassins and would happily kill Death just to see what happens.