Before we get into special weapons, I need to talk about the standard ones a bit. Intentionally or not, enemies in this game get a small degree of invulnerability between shots. This can greatly reduce the effectiveness of the buster depending on how fast the player normally shoots, as large enemies now take longer to kill, and when firing three shots in a row at one target the second will usually miss. There's still enough enemies that die in one hit to give the player a reason to use normal shots often.
However, in the case of the Charge Shot, the increased size, the number of enemies killed outright by it, the two ground enemies that move under normal shots, usefulness in boss fights, and what I think is a faster charge time all make it far more powerful than it was in the previous game. The only downside is that Mega Man loses the charge when hit, which balances it a little in boss fights but has little effect in the stages. Combined with the fact that few enemies appear outside of Mega Man's reach and the overall ease of this game, this means that the player has less need for special weapons than ever before.
This uses one energy point and creates three stones that swirl around Mega Man while moving outward. Only one can be used at a time, it's very difficult to hit with, and the only enemy weak to it is the moving spiked walls in Napalm Man's stage, which are also weak to half the other weapons. It was a stretch to find any screenshots where the multiple hits were at all helpful, and I wouldn't recommend using this anywhere except maybe against Charge Man.
As screen wipes go, this is a pretty good one. It costs four points, usually deals one damage, flipping over any enemy it kills and sending it off the top of the screen, presumably into space. It works instantly and enemies killed by it can't hurt Mega Man on contact, so it's great for clearing out groups of weak enemies, and can also kill Pukapelly in one shot. It also works on any projectiles that Mega Man can destroy, so it's not bad for wiping Yudon out either if you don't mind wasting it all on him.
There are many enemies that Crystal can kill in fewer hits than the buster, but none that it particularly stands out against. The best use you'll get from this is the speed and extra size, such as for killing the small ground enemies. It breaks apart on contact with a wall, but this is more likely to result in a situation shown by the gif than to be helpful. Still, at a one-point cost it's not a bad weapon to use often.
This changes Mega Man's slide into an attack. It also removes his ability to shoot, so its usefulness is limited. It can take out Metall Mommy, Tatepakkan, and Twin Cannon, but it also allows Mega Man to move through most enemies and traps. This allows another strategy for avoiding Power Muscler and Jet Bomb (which isn't destroyed by it) among others, and makes it the only weapon that's helpful for Wave Man's stage.
However, Shield Attacker can't be dodged this way and will damage Mega Man if he tries it. It uses one energy point per slide even when you don't hit anything, which further discourages the player from leaving it equipped. It also doesn't work very well against Mousubeil, as they take two hits and the kick only connects once if they're moving toward Mega Man.
These fall to the ground and slowly bounce forward until they hit something. They cost one point, but their explosion is pretty small and they don't explode unless they kill something or hit a surface they can't damage (anything that a shot would normally bounce off of). The advantages to using these things are that three can be shot at once, and they will quickly kill three of the strongest enemies in the game: Power Muscler, Cocco, and Yudon.
I love how this changes fighting Yudon, as it kills him in one shot but you'll need to shoot or dodge through the homing missiles to get close enough to drop one on his head. Unfortunately two of the three Yudons we've seen are in Napalm Man's stage.
This creates a moving wall of water that blocks enemy shots and moves through anything it kills. Unfortunately it can only be fired from the ground, there's almost nothing it the game to use that last property against, and even less use for its defensive potential. It does better than a Charge Shot against Metall Mommy (though it still leaves one baby), works well against Subeils when you have room for it, and can kill Mousubeil in two hits in a pinch. That's right, both ground-only weapons are weak against Mousubeil; Crystal, Napalm, and Gyro all take them out in one hit.
This creates the usual shield around Mega Man for two energy points, and can be fired forward. They only enemies with more than one hit point that it kills outright are Pukapelly and Napalm Man's spiked walls. However, it's reasonably useful against some of the weak flying enemies and protects the player from the falling crystals in Crystal Man's stage. Just don't try using it against Rembakun or Jet Bomb, as it can't defend against their projectiles. Otherwise it doesn't stand out, but blocking the crystals is reason enough for a player to consider grabbing it early.
Gyros move forward slowly, then move up or down if the direction is pressed. This is one of the best weapons to have equipped frequently, as it costs one point and is useful against a variety of enemies. It can kill Power Muscler in four hits, Apache Joe in two, and hits anything on the screen if aimed well. It's the closest thing this game has to a Metal or Shadow Blade.
Rush Jet is earned from Gyro Man and is unchanged from Mega Man 4. I don't think I need to explain what he's good for again, so here's a fun thing you can do with him in Gravity Man's stage.
Super Arrow is earned from Star Man, and it's a great new item. It can stick to walls for use as platforms or acting as a trap for enemies, but the best thing is that Mega Man can ride it, and it's fast. It only moves horizontally, but if the player knows or anticipates that there's a straight path ahead it can skip areas in a flash.
It has few uses as a weapon, but can kill Power Muscler in five hits. Its energy use is weird, as it costs two points to fire but drains very quickly if Mega Man is standing on it. This means it can only be used once for skipping long areas without recharging it, but the upshot is that Mega Man can fire three at once and use them to gain extra height before riding one. We haven't seen much use for it as a wall platform yet though.
Super Arrow also has the odd property of affecting Mega Man after it bounces from a protected enemy, potentially screwing up a ride.
Beat is our reward for finding the hidden letters in each stage. Once summoned, he dives toward enemies and returns to Mega Man, or hangs out over Mega Man's shoulder if there's nothing to attack. He uses two points of energy each time he hits something and can score multiple hits quickly on large enemies. He usually deals about two damage per hit, but can drain energy fast. Mega Man can shoot normally while Beat is in use, though only two shots can be on the screen at once and he loses access to the Charge Shot.
Beat is a fantastic weapon to have out at all times as Mega Man can still attack, and by carefully picking off weak targets that Beat is going after you can keep him in use for a long time. If he runs out and leaves Mega Man will be able to fire three shots at once again, making it easy to pick up more energy. Beat is useful just about everywhere, but since having him means we got all the letters there's not much reason to revisit the main stages, so we'll have to see how helpful he is in the final half of the game.
This is one of the weaker weapon setups of the series. The gimmicks of Stone, Wave, Crystal, and Napalm are mostly useless, though Crystal and Napalm at least provide extra damage. The upsides are that Gravity is good for its type, Gyro is a decent all-purpose weapon, Star protects against the most difficult platforming area of the main stages, and Charge at least gives us a new way to avoid some enemies without stopping to kill them.
Overall it's a handful of neat ideas that mostly don't work out in practice, but with enough uses that players can at least find something to do with them if they want to. Super Arrow and Beat are great additions though, and I like the new Rush Coil even though there's only been a couple opportunities to use it thus far.