YOU USED MAGIC!
No need to panic, Merlin. Just because Arthur caught you in the act ( so many jokes to be made here), doesn't mean you can't wriggle yourself out of it...
( FYI- A stands for Arthur, M stands for Merlin.)
1)
A:"Woah, did you just-?"
M:"No."
A:"But I'm sure you just-?"
M:"Yes, I did. But no."
(Then mysteriously flap your arms in front of you like a jellyfish and exit backwards from the room.)
2)
A: "You...used magic."
M: "SERIOUSLY? You notice NOW? Well guess what?"
A: (confused). What?
M: "Whilst we're on the topic of me doing impossible things, I'm also a self trained ninja assassin, I hold the world record for pie eating and I'm the only person to have been in so much trouble with the royal family and live. I'm cool, deal with it."
3)
A: "Are you... Are you a sorcerer?"
M: "No. I don't have a pointed hat."
(Magic up a pointed hat that is blue and covered in stars.)
M: Now I'm a sorcerer.