Summon Planetar/Dark Planetar is a very, very good spell. Better than Gate, and DEFINITELY better than any of the wizards Elemental summon spells. For all intents and purposes, Summon Planetar is like adding an uber-preist in spell casting ability to your group that is immune to normal weapons. They have a nice resistance to magic, and are darn good in melee to the point of having mad ninja skillz... Oh, and don't forget the mess of hit points, they can take a beating and still manage to somehow win the day for you.
Comet... the name speaks for itself. Calling forth the fist of gods without risk to you or your party is just plain cool. It inflicts high fire damage (duh), and more importantly knocks out and blasts away anything in the area of effect (30' ft. square). Even dragons can get blown away by this heavenly strike. Leaving you poised to move in for one full round to wail away on the beastie.
Energy Blades is another nice one. It can summon up to 20 blades that you fire at 5-10 a round (depends on if you’re hasted or not, I think...) I've only had to use it once, but when I did I was impressed in the insane amount of damage it could inflict in a short amount of time. Your wizard is seemingly quite proficient with these. However, some of the higher bosses are immune to the Energy Blades, and so you'd just be better off using that level 9 slot for a Comet or Summon Planetar/Dark Planetar.
Priest/Druid:
Elemental Summoning is THE BEST SUMMONING SPELL IN THE GAME! It normally summon up to TWO randomly picked normal elementals at once. None of the lesser garbage that you wouldn't let kill an Ogre... If you're lucky (IE: You're a high enough level) you can summon up to two Elemental PRINCES at once.
Greater Elemental Summoning is the Druid-specific upgraded version of Elemental Summoning, the priest spell. It is good in that it summon a Prince each and every single time. But you only get one...
Energy Blades? See above, but replace Wizard with Priest.
Paladin:
Greater Whirlwind is the wiggedy shiznit, ESPECIALLY if your have a Carsomyr+5-6 or Flail of Ages+3-5.
Summon Deva is nice to have, but it isn't vital. It is good for variety, that's about it.
Hardiness is also nice, but you don't need it. It can be handy to have around but you won't be using it that much.
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Stick to those skills (especially the top mentioned in each catagory) and you shoudln't have much trouble.
