I beat Magus sisters, on to Valvalis. I'm sure I'm missing some key drops in the Tower. Cid is still 100% useless. Cecil's turning out to be pretty worthless in this battle, too.
Cid was extraordinarily useful for me for the Magus Sister battle. Mute Arrows are nice this time of the year.
Okay. Clearly missing a pretty big piece of the puzzle here.
There isn't really a trick to it for the most part. Valvalis was redesigned to emphasize defensively to what she should have been... which is to be virtually invincible in her tornado form. Additionally, I've extended her original partial magic immunity (in tornado form) to total magic immunity, which is very appropriate for this battle.
Offensively speaking, I've intentionally selected a particular elemental to take advantage of her spell power (which was generally focused on one semi-avoidable spell at the moment) and to see if you did the treasure hunting. The key to the status attack (not her physical attack) is making sure you bought/kept some of that armor from a while ago... those EvilTwins should've given you that hint. Additionally, those doll drops are a good source of free protection. For countering Slow... Haste counteracts only half of Slow, but costs a little less than half of Slow... so it's still relatively effective (at least keeping your guys close to normal speed)... except that it accelerates Gradual Petrification (Slow obviously slows it down)... It's a fun conundrum.