Key notes about Magmog;

Positioning is key. Predict her moment turn one by positioning your members based on their fire resistance, she will move to Moria Flame (Fire breath) them turn one. Make sure each member is able to get into their position turn one, otherwise prepare a Dhreller or a Boombot to take their place.

Cooling. Remember you need to use 5 water spells to remove her flaming buff, which removes her chance to reflect damage, and cause a large chunk of damage if you behind your turn standing beside her. This should be done first turn always.

Cooling part 2. Once her cooling buff turns to <1 Turn you need to hit her with a fire attack to extend the duration of cooling. This can be repeated as many times as needed.

Ignoring her spawns. I feel the best way to deal with her Gobbalrogs are to ignore them, and maintain your position, it's important to burst down magmog quickly because she is the main threat. No matter how many Gobbalrogs spawn, if she dies, they all die.

Your eni is the best Doctor. Remember you can remove Concussion as many times as you need to with Enirazer; but remember you can only cast it once per turn, so make sure you use it wisely.

The Doctor always needs a companion. If you're running a sac or a Panda, make sure they look after the Eni at all costs, you're going to need him/her when it comes to Cata time.

Each turn, it gets a little bit hotter. Remember each turn you're going to take a set amount of damage per turn, this damage increases each turn the fight goes on, so try not to stay in there for too long.

Spells;

Moria Flame: which is a cone shape and fire based. (She will use this turn one always)

Meteor: This attack is earth based, and has an AoE similar to Devastate (Need to confirm this) and has a chance of summoning a Gobbalrog.

Bite: This attack will be very rare if you position correctly, it takes a large chunk and is quite dangerous, you need to be standing on the middle square of her for her to be able to use it. (I'll double check what element it is when I can)

Cataclysm; This attack is used when she drops below 3000~ or so HP, it can hit everyone on the map, it'll destroy barrels and other mechanism and hit you with fire damage. It's random how many times any one character can be hit, always try to keep everyone at high hp before this phase.

Usatei's Tier List

This list is entirely my own opinion, I don't claim for this to be fact, I just want to give you a good idea of what to use to build a strong team in my opinion. 

God Tier;

Panda - Map manipulation, tankiness with barrel, ability to protect the eni, Colling and debuff of resistance

Iop - Their punches hurt, their jump gives them great mobility to keep in position.

Enu - Cooling, Prospecting, tons of movement with Dhrellzerker, tons of damage with Dhrellzerker

Eni - Did somebody call for a doctor? Can cool with water and fire easily, Enirazer is a must.

Shiny Biscuit Tier;

Osa (Dragon) - Amount of movement they have, can gust into and out of position, really great damage

Sadida - Tanky, can stabilize themselves, Can heal allies, can cool and gust people/mobs into and out of position.

Sacrier - Sacrifice is great, very tank, can handle anything mog throws at them (Earth), great map manipulation and can deal with Gobbalrogs well.

Rogue - Tons of damage, really good movement, boombot = brobot (Can cool phase 2 of cooling with his fire attack) Great burst with fuss

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Because I haven't mentioned a class dosen't mean it's bad to use in mog, you can take anyone to magmog, the most important thing is to have fun!

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-Usatei