Ohh Kitru I really like the ideas you came up with in that last paragraph.

I don't care for the hostile undertones, but.... hehehe

Like I said, its hard to balance this idea without an practical test to see what's up, but I think you might be over and underestimating a few things:

Enmity:
- Flash is going to use 212 of roughly 3400mp, which is a 6% decrease in the mitigation your mana will provide you. That MP is replenished QUICKLY, or a flash spam could be used in concert with one of your MP regen abilities to get back up there.
- Concurrently, you won't NEED to flash spam unless you are in WP doing speed runs, as your enmity increase should be huge. Let's examine:
RoH Combo for PLD:
o Fast Blade = 150 potency = 150 Enmity
o Savage Blade = (210 potency x 3) = 630 Enmity
o Rage of Halone = (280 potency x 5) = 1400 Enmity
Total of 2180, or 726 per GCD
MB Combo for MYS:
o Fast Blade = 150x140% = 210
o Riot Blade = 210x140% = 294
o Mystic Blade = 240x5x140% = 1680
Total of 2184, or 728 per GCD

wwwhhhhhaaaaaaatttt!!!! While it might be 41% of the MYS's own RoH combo, its slightly over 100% of the PLD's RoH combo.

Also, think about this. RoH > RoH > RoH = 700 enmity per GCD, instant 700 enmity on each of 3 targets! MYS would be weak on snap AoE aggro, but ridiculously strong on single target aggro and single target tanking.

Mitigation - I'm not willing to do the math, and I honestly don't think its worth your time either, but I think you are overestimating the mitigation you get from your mana. Damage still goes through the MYS. Think about Titan, as everyone knows that fight. 4.5k MB, even if you are at full mana, will eat your 3.4k mana, and still do 1.1k of damage to you! Leaving you to scramble to get some mana back to mitigate the next attacks. If you had 1000 mana, it would allocate 30%ish of that damage to the mana pool, meaning 1300, i.e. it would mitigate 1000 dmg, leaving the MYS to eat 3500 dmg. The attacks TAKE your mana away...so the biggest shield you can accumulate against a large attack is your mana pool - if you look at the crazy hits in coil (unmitigated 8ks), the MYS is still gonna take 5kish of that (with a 3400 mana pool). Correct me if I am missing something huge here.

RE: Gear - Well...if you stack up PIE, you are going to lose vit and strength, so I fail to see a problem...and MYS armor, if it follows other tank armor, just wouldn't have it on it...Even if you can get your mana pool above your hp pool, hits will still eek into your hp pool, and you will die REAL quick on a serious of fast and hard hits with no chance for your healer to do anything about it.

RE: Mana Regen - I hardly thing 4%/tick is gonna break the game, lol.

RE: DPS Stance - Good point. I don't think that going from 120 to 138 dps is going to make or break a dungeon though... Seems silly to nit-pick that.

RE: CDs - Yes, Mystic Ground is stupid, but the text reads it goes UP to 170kish, and the rest of it was poor written and thought out. Dumb ability, not a good idea. I'm sorry : D And yeah, I guess I would just reduce Ramp/Sent, because I feel like if you leave those in there you are SUPER OP'ed. Some reduction to balance them out I think is necessary, so I re-thought removing them.

And again, this was mainly just for fun and for a basic idea : D, I still think it could be made about as viable as a WAR is right now (hehe), and managing a mana pool as a shield sounds very entertaining to me.