Some of the latter spell combos can be a bit hard to remember but for the most part they make sense.
Its been 15+ years and I can still remember a handful of combos, like Zan+watt = blizzard storm (prolly wrong name), foi+ zan= firestorm. Demi and wren have a combo which is good against robots.
You don't need to know all the combos, in fact the less ya know the better. Ya throw together an attack plan then BAM random combo that kills everything