Final Fantasy VII Guides and Walkthroughs
MP Absorb is one of the few Materia that you can almost never go wrong with leveling a ton of. It can be paired with the most common attacks you use on every character in your party or paired with a Master Materia so that all spells or abilities when used will restore mana to you.
It's possible to pair HP Absorb and MP Absorb together too. If you want Knights of the Round to absorb both HP and MP you'll need two copies of Knights of the Round and a copy of each HP and MP Absorb. In two separate paired Materia slots stick Knights of the Round with both Materia and it'll both heal you and restore MP! Note that this can be done with many other Materia combinations too and this is how you get the most powerful Materia combinations of all.
Where to find MP Absorb Materia:
Wutai - During the Wutai Side Quest you have to open a treasure chest with this Materia in it so Yuffie steals it from you
Useful MP Absorb Materia Combinations
MP Absorb + Alexander: One of the earliest useful combinations you can do with this Materia. Alexander does a lot of damage for little MP so they make a good pair
(Deathblow + Added Cut) + (Deathblow + Steal as well) (Deathblow + MP Absorb): Your Deathblow will strike with an additional melee attack plus have a chance to steal from the target. You can add another Deathblow + HP Absorb combo to this if you want.
(Counter + Deathblow) + (Deathblow + HP Absorb) + (Deathblow + MP Absorb) + (Deathblow + Added Cut) + Cover Materia: This will make it so each time you counter with Deathblow and that Deathblow will restore HP, MP and also deal a follow up regular melee attack.