First of all, Duo is added to Megaman, Protoman, and Bass as a playable character. Each character now plays a bit differently from the others as well. Bass can air dash and Duo can perform a shoulder charge.
A bit more is added to the story as well; Wily is on the loose, Roll is missing, and some special upgrade parts of Dr. Lights have been stolen. You must choose a one of those three objectives. You'll eventually accomplish all three, but the course you select again determines what robot masters you fight. Also different courses give you different extra abilities when you aquire Light's parts.
Unlike Power Battle, Power Fighters has different endings for 2 -player games as well (Power Battle just showed each player's ending individually in a two player game).
Sky Base
Course 1: Gyroman
Course 2: Shademan
Course 3: Airman
Pyramid
Course 1: Plantman
Course 2: Stoneman
Course 3: Pharaohman
High Rise
Course 1: Centaurman
Course 2: Elecman
Course 3: Quickman
Lake
Course 1: Bubbleman
Course 2: Diveman
Course 3: Geminiman
Volcano
Course 1: Heatman
Course 2: Slashman
Course 3: Napalmman
Bubbleman: Keep your distance from Bubbleman, for when he uses his Bubble Lead. He may call Snappers, but other than that, he's no problem. He's weak against Shadow Blades.
Heatman: Heatman fights similar to how he did in Power Battle. You'll need to stay on your toes and use the Bubble Lead to cool him off.
Plantman: Plantman also uses similar attacks to in the previous game. He's weak against Atomic Fire, but the odd way it works in this game makes it hard to be effective. If it gets too tricky, just use your buster.
Gyroman: Although there don't appear to be walls, take advantage of the wall jump to dodge the numerous Gyro Attacks he throws out. Gyro will also try ramming you; rapid fire him to drive him off. Use the Plant Barrier on him, then switch to your buster when it runs out.
Centaurman: Wall jump is once again your friend. He likes to charge here and there, and he'll also use a spear on you about halfway through the fight. Gyro Attack is his weakness.
Mad Grinder: The Mad Grinder from MM7 is back as a boss enemy. He has several nasty attacks, including crushing you under his huge wheel and causing quakes. Hit his head with Centaur Arrows and take advantage of wall jumps. Get close to him before firing the Centaur Arrow to make sure it hits.
Shademan: Shade fights much as he did in MM7, but he mixes up his attacks a bit, making him less predictable. Use Rolling Cutter on him and slash him up.
Stoneman: Stoneman likes to play defensive, creating stone walls to block your shots with. His Power Stone in this game consists of sending a huge stone hand across the ground. He can also stomp the ground to make an earthquake, so be ready to jump when he leaps high. He dislikes the Noise Crush.
Elecman: Elecman likes to shoot lightning all over the place; either straight forward, angled down, or across the floor. Get him with the Power Stone, however, and he's grounded.
Diveman: He'll send his trademark Dive Missiles at you, as well as set underwater mines. He may try his ramming attack as well. All of them are easy enough to evade. Fry him with Thunder Beams.
Slashman: Slash is all over the place, playing evasive and slashing you when he's close, as well as trying a rolling slash. Dive Missiles do a nice job of tracking him down.
Yellow Devil: The Yellow Devil returns once again, and he's nastier than ever. Quite agile for such a large enemy, the Devil bounces around a lot, and unleashes a huge array of attacks. He's once more weak against Thunder Beam; get up close so all three beams hit him, dealing three times the normal damage.
Airman: Airman doesn't do much other than his familiar Air Shooter. He may throw in a tornado attack much like Storm Eagle's, or sucking debris toward him and blowing it out again, but it's not as likely. He can be beaten down easily with Super Arm.
Quickman: Quickman can be tough. He zips here and there, throwing Quick Boomerangs the whole time. He may also do a dash attack. He's hard to avoid, so you want to beat him quickly. Unfortunately, there's no Time Stopper to save you; he weak against Air Shooter here.
Pharaohman: Pharaoh's another formidable opponent. He fires the Pharaoh Shot that arcs upward, then unleashes his powerful Pharaoh Wave. He can also block shots with a shield, sending your attacks back to you as more Pharaoh Waves. Keep moving and smack him with a Quick Boomerang whenever you get a chance (Quick Boomerang sucks in this game, you can only fire one at a time, and it uses way more weapon energy than before).
Geminiman: Geminiman fights a lot like in MM3, starting out fighting with a clone, then switching to his Gemini Laser later on. Take advantage of two targets and hit them with the two-way firing Pharaoh Wave.
Napalmman: There's little difference between this fight and the Power Battle fight. He's even weak against the same weapon; Gemini Laser.
Mech Dragon: The Mech Dragon returns from MM2. If breaths fire and can spawn baby Dragons. You want to hit it in the head with Quick Boomerangs, and you should have the super jump part by now, so you can super jump to avoid the attacks and get high enough to hit it by holding Up when you jump.
Dr. Wily: Doc's got a big grotesque skull head to attack in, and it's fully loaded. It fires standard plasma bullets, and also shoots bombs. The mouth will shoot a bouncing shot, and later a huge beam. He also spawns a countless supply of enemies to help him (Shield Attackers, Flying Cannons, or Baby Mech Dragons depending on what course you're on). You want to aim for the eye or the mouth, wherever Wily is at the time, and use, depending on your course, Bubble Lead, Slash Claw, or Super Arm. Wily will then appear in his saucer with the timer counting down, like before. Again, there's no major penalty for missing him, but your final score may suffer. You want to use on this part either Shadow Blade, Thunder Beam, or Air Shooter.
Protoman's Ending: Dr. Light tells Protoman that there's some kind of power imbalance inside him, and that it'll kill him unless it's fixed. Protoman refuses to have Light work on him, though, and leaves. Is Proto's fate sealed?
Bass's Ending: It's much the same as Bass's Power Battle ending, but Wily goes a little more into his creation of Bass, and he also shows us the new robot he's working on (it's apparently Zero). Bass thinks it's a ridiculus girly-looking robot, but Wily says that he's way more powerful than Bass or Megaman...
Duo's Ending: Duo talks with Dr. Light, saying he found more of the Dark Energy, then says he'll be returning to his home world. It ends with what's obviously an advertisement for MM8.
Unlike Power Battle, other endings are available with a two-player team.
Megaman and Protoman's Ending: It's mostly like Megaman's usual ending, only Protoman appears as well to provide moral support.
Megaman and Bass's Ending: Bass says that now that Wily's out of the way, it's time for him and Megaman to fight it out. Megaman is reluctant, but eventaully gives in. It ends with Megaman and Bass about to exchang Street-Fighter-style moves.
Megaman and Duo's Ending: It goes much like Duo's normal ending, but he has a brief conversation with Megaman, saying he'll leave to protection of Earth to him now.
Protoman and Bass's Ending:
Bass declares that he'll fight with Protoman after he's through with Megaman. Protoman accepts the challenge, but says that he'll never defeat Megaman as long as he fights for selfish purposes (it's almost a mirror image of what he says at the end of Megaman & Bass)
Protoman and Duo's Ending: It goes much like Duo's normal ending, but he has a brief conversation with Protoman, asking about his relationship with Megaman. Protoman says he has no relationship and just wants to be alone, but Duo doubts that.
Bass and Duo's Ending: It goes much like Duo's normal ending, but he has a brief conversation with Bass. He tells Bass that despite all of his bad-boy talk, he feels that there is good in Bass, and tells him to think about it.
