Mage Arena
Starting Point: In deep member wilderness, there's a hut east of the Pirates' Hideout with two webs blocking a lever. Be careful here, many PKers camp near this place. After pulling the lever, talk to Kolodin.
Description: Prove yourself worthy of this blood thirsty wizard by surviving the trials of the mage arena and he will teach you new spells, more powerful and destructive than any seen before in the world of RuneScape...
Requirements: 60 magic, 37 prayer strongly recommended
Difficulty: Medium-Hard
Items Needed: Magic equipment, runes, food, prayer potions (optional).
Reward: A god cape of your choice along with the staff of the corresponding god. Ability to use god spells if you have cast them in the mage arena 100 times.
First of all, you guys should know that this quest gives no quest points. It is actually qualified as a mini-game rather than a quest.
Getting there and recommended equipment
There is a bank in the mage arena starting point, so you won't have to go through all of the wilderness with all the required items. Just bring a knife with you to the quest starting location.

You are not to bring any melee/range equipment into the mage arena. You are also not to bring mystic robes, splitbark, books, or elemental/dragonfire shield into the arena.
The recommended equipment includes: Gnome/Canifis hat, wizard robe top, Zamorak robe bottom, magic/glory amulet, prayer potions, a little food, either a fire, earth, or air staff (not battle or mystic staff), and additional runes to cast 100 fire/earth blasts. Don't try to use Iban Blast, it won't work here.
Fighting Kolodin
Bring all your necessary equipment, talk to Kolodin to start the mini-game.
You will now be teleported to the mage arena, Kolodin will attack you. He's easy to kill, you can 1-hit him.
After Kolodin dies, things get hard. Put on protection from magic now, and drink a prayer potion when you go below 20 prayer points.
With Kolodin's first form destroyed, you will face four more monsters. I'm not sure on the levels, but it's not like it matters.
Your second enemy is an ogre, third is a giant spider, fourth is a soulless, and final is a black demon. You can run in between any of these enemies, but you will have to face PK-ers. If you chose to run, talk to Kolodin again to resume your duel.
With all of Kolodin's forms defeated, walk into the sparkling pool northeast of Kolodin. Keep walking down the path until you see the statues of Saradomin, Guthix, and Zamorak. Pray to any one of these statues to get a god cape, then talk to the staff-seller in the beginning of the path for the corresponding god staff.
CONGRATULATIONS! (mini)QUEST COMPLETE!
Quest guide written by Angrymx.
In case you're interested, the spells are different.
Strike of Saradomin deals more accurate damage than all other spells when the spell "Charge" is in effect, it also drains prayer.
Claws of Guthix deals the most consistent damage and is a low-level mage's best bet. It lowers your opponent's defence, which makes it even more formidable for an all-rounder.
Flames of Zamorak is weird. Its accuracy depends on both your magic AND range level. This spell lowers your opponent's magic, which makes it good for mage vs. mage battles.
You can change god capes by dropping your current one and praying to a different statue.