Disgaea 2: Cursed Memories

You just fight and kill them all. Easiest way is to throw a mowerful or long range character clear across the map on the first round and destroy the clone geo symbols in the first 2 rounds, then mop up the enemies.

Which character are throuwn the longests?

Heavy Knights have the best throwing ability, to my knowledge. 6 panels, with an impressive vertical range. Adell, warriors and beastmasters have a 5-panel range, with varying height clearance.

level up in Cave of Ordeals 1 some (at least i passed the bill at about the same time as the city episode) and level up to around 60 for Adell and Rozalin

I just did this mission. Levelling up on the second level of that chapter ((Alche City, Grave of Alchemy) helps. (I was only two or three levels above your current level when I completed the level.) Upgrading your equipment is a good idea too.

On the actual boss map, line up and throw your guys to the end of the map with the cloning prinnies and the clone geosymbols. Blast the symbols (or the prinnes on the arch that clone) with magic. Then duke it out. Some character WILL get swarmed and killed.

Worse comes to worst, you can always start throwing prinnes, they *do* explode after all. Some of your guys may die in the resulting explosions. But the benefit of throwing your guys is that the prinnies will crowd around your guys at the end, so allies further back can throw a stray prinny and blow them to smithereens.

Death by exploding Prinnies, according to the board sticky, does NOT count as an ally kill. But you don't get experience or mana for it. Better then losing.

Make a tower of Knights and take out the Cloning Geo Symbols, then throw the Prinnies around at each other.

What i did was i just threw the prinnes at each other and they would all explode and kill each other

well basically i unlocked "cave of ordeal" and jacked my characters up and reincarnated them like 15 times each with genius... SO:Get all your characters that you have and stack them up and attack the geo stones then the rest is easy.
(my Adell has 5000 atk reincarnated and lvl 80 atm, got the game 2 days ago)

If you want to buff your characters up, go unlock "cave of ordeal" stg 1, kill one of the corner geo stones(i recommend going to settings->turn "FAST" geo panels) and then they all will all have less then 200 hp. Plus good way to get money.