MP Turbo Limit and the Cumulative Support Materia Effect
I am actually amazed I haven't seen this first part here before...
The most mp you can use in one go is 255, and (to my best knowledge) this can only be achieved via MP Turbo. This is mostly achieved (and is most useful) in one particular case - MP Turbo-Knights of the Round. For a measly 5 extra MP, you can guarantee every hit will cause over 9000 damage. This is useful when you consider that, at least for me, it was only doing around 5500-6000 per hit - that's an increase of around 39,000 in damage.
And, if you find any other materia that this can apply for - like Bahumat ZERO - then you can apply this elsewhere. I use it pretty much every game I play on FFVII.
And, here's the Cumulative Support Effect. Say you master a Fire, and an All is attached to that Fire. Now, equip that Fire in another pair slot, and attach a different support materia, like Quadra Magic. You can then cast Fire(1) on ALL enemies 4 times in 1, because there is a cumulative effect of support materia in this fashion. As the new materia levels up, the other Fire spells will also have both effects.
This is applicable to both magic and summons, and perhaps some command abilities. Very useful for, say, revive materia (Final attack + all) although it's usefulness can be lessened due to the usefuness of Mega-All later on as a replacement for all your normal Alls.
Either way, hope I helped.
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