So,
the most iconic characters of RuneScape,
which have enough of a story to be qualified as a proper Legend,
recognizable from outside the game by most players who played RS for at least a year or two and who could fit as a playable character in a card game (that means all Legends should be roughly equal in combat)...
...and for balancing's sake, I'll pick 3 mages, 3 rangers, 3 warriors and 3 "others"
-Wise Old Man
-Nomad
-Lucien (without rejuvenation, without stone of jas, maybe with or without staff of Armadyl)
-Zanik with God-slaying crossbow
-Any slayer master, but let's say Mor*ran because he's already selected anyway
-Some dwarven cannoneer (just to slap the multicannon somewhere, as a playable character. I dare anybody to question the dwarf multicannon's Legendary status.)
-Sir Tiffy Casheen
-Vanstrom Klause
-Thok (endless balancing issues with this guy but, whatever)
-Sandwich Lady, Jail Guard, River Troll, Tree Spirit, Drunken Dwarf and the others, in a team
-Gnome Child
-A swarm of default-look bots