"I'm sorry, I promised not to talk about your daughter becoming the King's Mistress, and here I am, talking about your daughter becoming the King's Mistress..."
"He leaned up against a wall, grinning broadly at me. His entire face seemed to be dominated by a large black leather fedora, that he wore low on his head. His hand seemed to be flipping a coin into the air, its golden shape gleaming in the morning sun. His body looked almost preternaturally thin, and his position on the wall would look painful to one who didn't know him. His entire presence seemed to scream out as an untrustworthy soul, but I knew I trusted him regardless. With my life, if necessary."
Sean is the tiny brain of Amber. Well, sort of. While his raw psychic power and skill are the lowest in the family, they still crush Joe Amberite by a fair margin. In addition, Sean has an iron will, able to hold out against incredible psychic punishment about as well as Mike. He's average with a blade for the family, on a level with Rod and Andrew, and a decent tactician... again, capable of crushing Joe Amberite. He's not massively strong but a skillful martial artist, and can take massive amounts of physical punishment, well above everyone but Mike and Dan, although far below Mike himself and a little above Dan.
Without a doubt, Sean is the master shapeshifter of Amber, beating out King John and Dan in body skill. This combined with his extreme durability makes him a bit of a Jack in the Box; he keeps popping up, jester's cap jangling, regardless of punishment. His pranks are legend. So are his gaffes.
Sean carries an extremely potent saber which he calls Regret, and which seems to be as nasty a weapon as you get short of Patternblades. He has taken the Pattern at the usual basic levels, and has some trump sensory ability.
After everything was sorted out initially, Sean vanished off into Shadow for some time, periodically keeping in touch by trump. When he returned, King John made him a member of the diplomatic corps. His current assignment, to the Canite states, has yet to end in horrible disaster.
Sean has expressed a wish to build up and keep his martial abilities. For this reason, Mike, Dan, and David frequently drag him into the gym to 'practice anti-shifter techniques' with. Sean's ability to take a pounding is very handy in these sessions.