Here's some that i've found work very well, not all bosses listed here.
BurnerMan: Use RockCubes or the Fanfare and place them in your top right and bottom right corners to block his burners. then use a LifeSword PA, or the TimeBomb+ PA a few times for an easy win.strangely, the best Soul to use here is Flameman's soul.
LaserMan: first use the NaviCust to equip Airshoes and Floatshoes since he breaks your area. DO NOT GET HIT BY THE BLUE PALM LASER!!!! if you do, your navicust doesnt have any of its effects. Try to keep moving during the battle and make sure you dont get in his row unless yu have a good chip to shoot him. Swords will be great here since he is usually in the front 2 collumns. WindSoul and ThunderSoul help alot, as does Searchsoul.When hes close enough to use it, fire the MetorRed giga chip at him. it does 300 damage wich is pretty good aswell as cracks a 3X3 area.
KendouMan:Make sure you have very few if any sword type chips for this fight, because close range fighting is his best.If you stay in the front collumn too much, he'll run up and stab you VERY quickly. try a HeatSprd or BubSprd PA, and the PileDriver. If you have the AirHoky3 chips, use a PitHocky3 PA on him.When he uses the move Training, 2 clones of him appear. if you have enough HP, then just let them hit you, if not then stay in your fr back collumn and move up and down continuosly until the Training attack ends.Dont bother attacking while this is oging on because youll most likely miss.
Shademan: This is for when you fight him in Undernet4 after completeing the Django event.when hit, he splits into 4 bats. he only takes damage if you hit the bat that Shademan is.so to beat him easily, use 3 AreaGrab or Metagels to lock him in his back collumn.then use any GunDelSol 1,2,3, or EX chips you have. its goood to have 2 or maybe even 3 of each. but DO NOT ATTEMPT THE PILEDRIVER!!! The Gundelsol's will do more damage all together than the PileDriver PA.try not to destroy the Greendata in battle too, because you get a Giga Chip from it.
Duo: Duo, the last boss, 4th hardest fight in the game.oh, the 1-3 hardest are 1)BassSP 2)ShademanSP 3)Bass. When you begin, youll notice Dup takes up the back 2 collumns. those panels DO NOT EXIST. Any chips that hit his area like AirHocy will not hit him.He is vunerable only when his red light on his chest is lit up. the only point that hurts him is the chest light.When he luanches the Mine and Missle, the Missle has 50 HP and the mine has 30 HP. Shoot them odwn or dodge.When a cone shape appears on his chest, he will fire a Laser. the laser go through barriers,auras, and Invis.it goes over your Center row.There are 5 rings that appear on the sides of the laser. the first is in you far right collumn. next is in the middle collumn, then the rightmost collumn, then the left collumn, then the middle again. DODGE THEM.its not very hard. when a 2X2 area flashes, Duo's fist disapears then slams down on the tiles. Though somehow, the tiles dont crack or break. its easy to dodge. When Duo'd fists dissapear, your back two collumns will flash and he will slam his fist through the collumns, then pull his fist back up through your front two collumns. Just stay in the far right collumn then move to the far left to dodge it. Now it gets tricky. Duo will begin firing many fists at your panels, 1 fist for each panel to be exct. when a panel flashes yellow, it will be hit. move to a panel that flashed yellow after the fist hits it. you wont get hit then. Also, this attack has a tendency to break panels.when the battle goes for awhile, he'll fire his face at your front 2 colluns. its not hard to dodge and i dont think it breaks the panels. You can tell when he will use this attack because he will fire 1 missle, 2 mines, then he will slam a 2X2 area twice with his fists. Good thing Duo is so easy to dodge his attacks, because they hurt, i mean REALLY hurt.Windsoul is good for this battle, as is Flame,Thunder, and Search.Gutsman has no use unless you have the RedSun chip because it will doan extra 180 damage.use any grab chips to get his only collumn for yourself. try not to use Sword,Widesword, or WideBlade since you wont be able to dodge the missles/mines that close. When Duo slams his fist down, move close and use GunDelSol's on him for good damage.Sadly, the PileDriver fails to do its normal damage because Duo covers the back collumn.all this said, Duo really isnt too hard if you know what your doing.Except for Duo SP, thats VERY VERY hard since hhe attacks waaaay faster.