KOS-MOS is a must-have whenever possible. Unfortunately for me, I thought Ziggy was actually useful for a while, and spent time developing him. My mistake...

My typical party was Shion, KOS-MOS, and Jr/MOMO, depending on the situation.

The only time I found the game particularly difficult was when I was rushing thru the first time around, and made it to the end in under 40 hours, and I was woefully underprepared for the fight. No Erde Kaiser, I was half the level I should've been, and I remember that I never realized something about upgrading AGWS units. I was in sorry shape, and surprised I got that far...