In trying to improve Arthur's chances of surviving a near-impossible match, Merlin magicks certain, uh, "special abilities" into Arthur's armour. Since Merlin himself has the mad hots for Arthur, the sentience he imbues on the armour does, too...

Merlin knows that getting off fastest when he's got some BDSM porno playing loud on the computer doesn't mean he'd really like to be that bloke, gagged and bent over and bound. Right?