Alright, time to look through our inventory. Hard Knuckle
Mega Man stops in place for a moment and fires his fist forward. It's slow, and can be directed up or down slightly with the D-Pad. Though it does more damage than the buster, its speed often prevents it from being useful. The best uses for it are killing Big Snakey (two hits), Bikky (one hit), and Tama. Tama requires a few more shots, but if you get close enough and fire rapidly you can take advantage of the way it stops you and hang in the air long enough to finish him. While it can also kill Hammer Joe in one shot, you'll need to time it well or get close. As a side note, most special weapons can destroy the hammers as well.
The Needle Cannon fires forward, the shots are quick, you can have three of them on the screen at once, and nothing is particularly weak to them. Sound familiar? The only advantage these have over the Buster during the stages is that they fire automatically when the button is held, so you can give your finger a rest in situations where you'll do a lot of shooting.
Spark Shock fires forward and stuns an enemy for a while. You can't switch weapons to kill it afterward and you'll still take damage by touching it, so using this on anything is usually just going to prevent you from moving forward and leaving you in the same position after it wears off at best. At worst, you'll end up in a position like the last screenshot because only two things can be stunned at once, after which you won't be able to shoot. The only uses I found for it were to get under Bikky and Monking without dealing with them.
The Shadow Blade fires forward, upwards, and diagonally, returns after a short distance, and only one can be on screen at a time. It usually does about two Buster shots worth of damage and can kill Bubukan, Bomb Flier, and Have Su Bee in one hit, though you still have to break the cloud. It works on everything, and has enough ammo that you could go through a whole stage with it. Though it's no Metal Blade, it's still a powerful advantage, being useful for enemies normally out of reach and plowing through enemies that would normally require two shots, like Petit Snaky. The one downside is that missing will leave you open for a while, though a returning shot can sometimes be helpful too.
This travels along the ground like Bubble Lead, except it's faster and can climb walls. It's not any better than the Buster against most things, but spamming it against Komasaburo and Tama will destroy their shots and climb after them. It's also great for the dark section of Shadow Man's stage, as it'll let you know where the floor is and kills everything along the way. What it doesn't do is kill Mechakkero (though it'll hit him in the air like everything else), the enemy which is too low to the ground for normal shots to hit, which is exactly what this sort of weapon is supposed to be good for.
This can only be used in the air, and it makes Mega Man spin around and damage whatever he touches. This is awesome when it works, but there are few places in the game where all of the enemies in the area are weak to it, and if they're not, Mega Man just takes collision damage. It kills Monking and Mechakkero though, so that's a plus.
This one bounces from walls at a diagonal, as shown above, but only one can be fired at a time and it'll bounce all over the place if you miss. It's also not usually strong enough to be worth the effort, and there aren't many places where the bounce mechanics work in your favor. It kills Komasaburo, New Shotman, and Hari Harry in one hit, and Monking in four. Otherwise, it's best not to bother with it.
Magnet Missile fires forward until there is an enemy directly above or below it, after which it will move up or down to hit that enemy, and two can be on the screen at once. This is great for just about anything not on level with Mega Man. The 2-bar cost forces players to limit their use, and it will sometimes track projectiles instead of what you want to hit, but it's otherwise useful for the same situations as the Shadow Blade with less risk of leaving yourself open, and is particularly helpful in Shadow Man's stage for two enemies that are otherwise hard to reach. However, for some odd reason it won't track Walking Bombs, though you can still hit them directly.
Unlike Item 2 and other incarnations of this power, jumping on Rush allows you to move in any direction at will. Mega Man can still shoot, but can only have two shots on screen instead of three. The energy will gradually decrease during use, but only while Mega Man is actually standing on him, so jumping repeatedly while moving forward will reduce the cost significantly. Otherwise, there's not much to say. Just use it anywhere that you wouldn't want to cross on foot. It's also kinda fun to turn the Big Snakey battle into a SHMUP.
Rush Marine moves in all directions in water. It can also jump out of the water, but can only move by jumping when on land. Since it can't even be summoned out of water, let's take a look at the one place we've seen where we can use it.
Gyoraibo is easily killed now and the goodies at the bottom are easily collected, but we're on a tight energy limit and there are only two refills along the way, both of which we need to leave the water for. This leaves us vulnerable to the Yambows, and there's not a lot of room to dodge in the water either. Killing the Yambows is an option, but that wastes precious time. After picking up the second refill, it's best to just use the platforms the rest of the way. An advantage of doing this with Rush Marine instead of switching out at this point is that it doesn't get knocked back when taking hits, so the last few jumps are relatively safe as long as you have the health for it.
While this section is slightly easier with the Rush Marine, it's still harder than most other portions of the game, and rather than feeling like you're skipping a challenge like with Rush Jet, it's more of an alternate path. Despite only being useable in this section (so far), I'd call that a success.