The Mantella - Introduction
There are six parts to the Mantella quest. Each part is accessed by solving problems and puzzles in the previous sections.
There are no dungeons that look like mating octopi here (yea!). But it's a pretty complicated problem and very easy to get lost. It is commonly believed that once you're into the Mantellan Crux, you're stuck. This is not necessarily so.
As long as you have a "Recall" spell anchored somewhere outside the Crux, you can get out. Getting back in is a tougher nut to crack. It is true that Nulfaga is a one-way trip. She will not teleport you back into the Crux if you leave. But there is an entrance in the "real world". In order to find it you absolutely MUST have a ship. It occupies the square just NW of the Small Ship (if you have a Large Ship, the Small Ship is northwest of you). Go Northwest from your ship until you get a message at the top of your screen. You are now in the square that contains the entrance to the Crux. You'll need to do some searching, but eventually you'll find a large square of land with a big rock in the middle of it. The door on that rock is the entrance to the Crux. When you click on it, you will land at the same spot where Nulfaga sends you. So if you find that you've bitten off more than you can chew and need to pack in some more training before tackling it again, you are able to leave and still get back in.
DANGER: I have done the entire Crux without having the Mantella Quest active. The sequence of lever pulls and such to move you from one section to the next is the same without having the quest active, but unless you have a "Recall" anchored outside the entrance, you cannot get back out. THERE IS NO EXIT FROM THE CRUX EXCEPT BY "RECALL" OR THROUGH NULFAGA.
In order to complete the Mantella dungeon you absolutely, positively MUST be able to levitate. Whether by spell, device or potion, you've got to be able to do it or you'll never be able to finish. If you belong to the Mages Guild or the Temple of Julianos you should have access to the item-maker by this point. The Assassins Guild and all temples (except Kynareth and Julianos) give you access to potion makers. You can buy the "Levitate" spell from the Mages Guild whether you're a member or not and the Mages Guild and Kynareth provide access to a spell-maker to make your own spells.
[Addition (5 May 2006): about six weeks ago I saw a post on the Past Games board at elderscrolls.com that showed how to complete the Crux without levitating. Jormungandr (the poster) said that he did it in large part just because I had said that it couldn't be done. I love it when people prove me wrong - it means that I learn something new. So I've gone and added his information on how to do it without levitating. The info is just a copy/paste from his post, so I'm not taking a lick of credit for his work, but am just making it available and adding my own congratulations for doing the impossible (and something I still haven't been able to accomplish.]
If you're a spell-caster, you should have some way of restoring your magica points. It's seldom safe to rest, so you might want to stock up on "Restore Power" potions. My solution to the problem was through the item-maker. A Daedric Dai-katana has enough enchantment points for Vampiric Effect, Magica Leech and Feather Weight. So whapping the bad guys not only heals my health, it also replenishes my magica (almost all critters in the Mantella dungeon can cast spells). That just leaves fatigue to worry about and "Heal Fatigue" is an awfully cheap Restoration spell.
There are lots and lots of Daedra (Lords, Seducers, Fire, Frost) running around this dungeon. All of them like to toss spells at you. Something to reflect or absorb these spells is almost a necessity (unless you're very masochistic). "Shalidor's Mirror" is the most potent version of Spell Reflection. By this point, your odds of successfully reflecting a spell with it should be close to 50%. You can make your own custom spell in the spell-maker, you can enchant an item, or you can get an artifact to do it. If you turn the totem over to the Emperor you'll get Warlock's Ring which has Spell Reflection as one of its powers. If you turn the Totem over to the Underking, you'll get the Necromancer's Amulet which will absorb spells.
Bows are very handy. Bring one and lots of arrows. On the subject of weapons, enchanted weapons have a nasty tendency to break at the least opportune moment. Make sure your weapons and items are in "New" condition before you start and you should have no problems. It is always a good idea to keep a spare weapon or two handy, but especially here. You will not be able to access your wagon, so whatever you brought with you is all you have. Don't count on picking up weapons from the critters in here. Most of them only tote money and potion ingredients. Some don't have anything.
Lastly, make sure that you have everything you need, that you have trained all you're going to train and that you are not on the verge of picking up another level. Once you're in, you're in for the duration unless you want to kiss the quest goodbye.
OK, now that you're armed to the teeth and loaded with magic stuff, it's off to the hunt for the great Magical Dingus of Ultimate Power.