Mega Man 4/Adapters, items, and weapons

Weapons
Rain Flush: Get from Toad Man. Launches a projectile upwards which explodes, releasing acid rain upon all enemies on the screen. Not too powerful, but it does harm every vulnerable enemy on screen.

Flash Stopper: Get from Bright Man. Freezes all enemies on the screen, allowing you to blast them with your arm cannon for the short period they are immobilized. Doesn't work on bosses (with one exception.)

Pharaoh Shot: Get from Pharaoh Man. Shoots a small fireball, but can be charged up like your Arm Cannon to enormous size, vastly increasing its power.

Ring Boomerang: Get from Ring Man. Fires a short-range ring-shaped boomerang. Powerful, but lacks range.

Dust Crusher: Get from Dust Man. Fires a junk projectile that travels the length of the screen. Useful at a distance, and stronger than your regular cannon.

Skull Barrier: Get from Skull Man. This game's obligatory "orbiting barrier/shield." Protects you from weaker enemy attacks, and works as a weapon when you walk into a vulnerable foe.

Dive Missile: Get from Dive Man. Missiles that seek out foes on the screen. Very useful since they track down the enemy, so you don't have to aim.

Drill Bomb: Get from Drill Man. Fires an exploding drill-like projectile straight ahead. Can be detonated early with the attack buttom.

Adapters and items
Rush Coil: You start the game with this. Identical to its incarnation in the previous game. Jump on Rush's back and a springboard emerges, allowing you to reach new heights with your jump.

Rush Marine: Get from Toad Man. Again, just like its previous incarnation. Can only be used underwater, in two stages only: Dive Man's and the first Skull Fortress stage.

Rush Jet: Get from Drill Man. Unfortunately, it has gotten a massive downgrade from the previous game, and Rush automatically goes in one direction when you board, rather than you having precision control over him. Still he can be useful in a number of situations.

Wire Adapter: Found in the Dive Man stage. By looking up, Mega Man can fire a grappling hook to pull himself to heights even greater than those reachable with the Rush Coil.

Balloon Adapter: Found in Pharaoh Man stage. Mega Man creates inflated platforms that can be used to reach new heights. Very useful in situations when you might need more than one jump or foot hold to clear an obstacle.