I suppose it is the brimhaven agility arena? Wear the steel platebody, maple short and a wildy cape and do the emote called cheer in the arena. You might be attacked by a lvl 107 btw...
dont use magic, waste of runes... use a dds and spec him. bring a few sharks and a pray pot in case he gets lucky but you probably wont even need to eat (hes really easy:p)