Level 1-55 magic for free.
Take an armor helm, plate, platelegs, kiteshield, air staff, any vambraces (just get your attack magic bonus to -68), go to fist of guthix, auto cast the highest attack spell you can onto your opponent (note, at -68 magic bonus, your spells will splash every time, but every time you splash, you get 8-15 magic xp depending on the spell you casted). This way, you don't level hitpoints or combat, and you can have 55 magic at lvl 3 combat absolutely free. You can just afk while your character autocast splashes until your opponent gets 5k charges.
This will take at most 2 days, also depending on how your opponent responds to you (he runs, he stays at the center etc).