Scene 5 - 'The End of Red Skull'
Another shooter segment, with the enemies from the second stage returning, now more powerful than before. Wasp is also back, and you'll eventually find the giant laser, which just requires a lot of shooting and punching to be destroyed. There'll be three guys there when you land, and the next wave consists of three gunners, a green and an extending fist, but they can all be easily sorted.
The floor will give way and slide you to a lower level, where Crossbones taunts you and flees, leaving you to fight two control operators. They don't have more in the way of attacks other than grabbing, punching, and flying kicks, though there are sawblades that run along the lines in the floor, which can only hurt you and not the baddies. Aside from that, they shouldn't be too difficult.
After Quicksilver drops you another 20HP item, you'll face two beetles, a gunner and two extending fists before you fight the mask wearing punk.
Crossbones can stab and throw his knives, drop mines, shoot three bullets and jump like an athlete. I hate to keep repeating it, but none of the attacks are particularly dangerous, and as usual, shooting him from above works well. Be sure to nab the 20HP behind his desk.
Things aren't over yet! Red Skull gets away on a platform, so after fighting another wave of gunners, extending fists and whatnot, you fight the man behind all these crimes. He simply runs around and tries to punch you, and takes tons of damage from your projectiles, so simply float above him and do what I suggest so much.
He then grows thrice his size and it's revealed this is yet another robot: Mech. Skull, while the real Red Skull laughs behind a glass dome. Mech. Skull can shoot a green laser from his chest, deploy his lower arms to chase after you, spin around while firing bullets from his fingers, create whirlwinds, have two fireballs circle him, including the punches and jumps. Your punches barely scratch him, and the only time you're safe being close to him is when he spins around machine gunning everywhere, so pump him full of projectiles and hope for the best.
If you succeed, congrats! Have an ending.