i actually don't know the exact formula -- but here's essentially how it works (for green flow, in PvP)
*remember mana here is base max mana, it does NOT include mana from gear)
damage = (50 + (mana * 2.5) - opp_dex) * random number between 0.00 and 1.00
for example: if base mana is 200 (probably level 120-180 mage, depending on stat distribution)
damage = 50 + (200*2.5) - opp_dex) * random
SIMPLIFIED to (50 + 500 - opp_dex) * random <we will say he's fighting an archer with 150 dex>
SIMPLIFIED to 400 * random meaning each attack will cause between 0 and 400 damage
NOW, for fun, let's look at my idea, with the same characters (fully equipped level 125+ mage)
same base mana of 200, PLUS 180 from equipment = mana of 380
now damage = (50 + (base_mana*2) + mana from gear + dex - opp_dex) * random
SIMPLIFIED 450 + 180 + 2 - 150 = 482 * random... meaning damage will be from 0 to 482... actually better at this level (assuming fully equipped)
the real benefits here, are that at low levels, mages would benefit, at very high levels, mages would be nerfed some (also, there NEEDS to be a way to control how mages attack monsters, right now, they always hit at full damage and it is simply unfair to the whole game IMO, so having the opp_dex reduce in PvM is a MUST) AND, this way the mana from gear actually is important, so gear is more valuable
lets look quickly at a level 1000 mage (just for fun) - for current and suggested formula, we will use a mage with no dex (2) and 200 armor and 1800 mana
CURRENT -- 50 + (1800*2.5) = 4550 -- so average damage (0 opp_dex) will be 2275 after multiplying by random
SUGGESTED -- 50 + (1800*2) + 180 = 3830 -- so average damage (0 opp_dex) will be 1915 (around 15-20% reduction at this level) ... and again, the low levels would benefit, high levels would be nerfed a bit
Anyway, I hope this explains it a bit better, please continue with any support, questions, or concerns

-- to be honest, I'm not sure that dropping from 2.5 to 2.0 multiplier is enough, but I hesitate greatly in fear of nerfing the mage too much... as MadMikael said here (and I and others have said elsewhere) it's difficult to balance because the mage is the only class with a multiplier at all, which he uses ALL THE TIME (as opposed to other classes only using skills half the time... this is why I suggest allowing skills to act independently from each other)
BTW - I added ideas 12-15 to top post
