I was wondering what was up with him regaining HP at times. The shotlock that worked best for me was Bio Barrage. I also read about the abilities thing. I'll try again tomorrow when I have got my patience back.
Btw, this may be a dumb question...but do you have to fight VS and MF as all three characters...?
He actually has two ways to regain HP, either by rewinding time (then even the music runs backwards) or by using renewal block.
Yea, Bio Barrage and Thunderstorm work best as they have the lowest overall lock on count, but there's always the danger of him using Renewal block mid-attack.
If you're aiming for 100% Report completion then yes as each character has an entry for facing the secret bosses.
MF with Terra is truly a pain. I remember dying over 70 times when playing on the PSP until I finally got this sucker with Terra.
Aqua has the advantage of her barrier for defense while Ventus is very fast and nimble, but Terra has really the short stick with this boss.