The best boss to start of betting is the jungle one, the soldier stonekong (or something like that) when you get to him, immediately run to the left, jump to that platform, be axle. you need to get to that section within 1 second or take a lot of damage from his charge. just stay on a different section then him, 1 of the other 3 platforms. keep shooting him. if he shoots his shield around the ring, when it gets close jump and hover. when he jumps onto the power core, and he throws the 2 rocks. switch to Zero and double jump over them. keep shooting him until he dies. (tip, after getting the first of power up, firepower, speed, special, upgrade the firepower and speed at least once with axle. that makes the attacks stronger and you can fire faster.
the next boss to go to is at the grand cercuit. the pig bull thing. when he charges, jump and hover, or double jump with zero( doesn't always work well). just shoot him and watch out for his grenades and the grenades from the outsiders. keep shooting him until he dies. when you see a ball form at the center, run toward the outside edges of the arena. if they are close enough to hit you, jump over them. when you win, save and go to stage select, or power up if you got any.
you will either get mega man after you beat him down, or it might take 1 more stage to win/lose at. if you get mega man then,
go to the under ground facility. his charge up shot goes through enemies, and does major damage to bosses, when not leveled either.
once you get the giant armor suit, try not to get it destroyed, you'll need it in the next area. once in the chamber with the green liquid all around, you can jump into it, if you have the suit, and not die. rescue as many people as you can then go to the next are. at this giant are, you have to kill many other ride armor people, the best way is to get on top of one of the large column and charge up and shoot them when they try to launch missiles, since magmas charge up shot goes through terrain. once they are killed, you fight the boss in a force-fielded area. just stay as far away from him and shoot him until his armor is destroyed. then he jumps out, harder still. he will continually jump around making it hard to shot him. just charge up and rotate the camera to keep him on screen, when he gets remotely close release and charge and get away and repeat. if he does his volcano kick (or something simeril in name, you will here him say something then he jumps at you, wither boost or jump and boost away. continue this to kill him. after this boss, or before when you have mega man, go back to the jungle stage with zero and mega man. at one of the giant statue heads, you will need to double jump to the left onto a branch, when the head is at its highest, then you will get magmas boots, lets you glide.
it sometimes works best to go to some stages where you can never win at yet, to rescue as many people as you can, and get mega man parts, only 4.