Top Tier:
Fair -Great for approaches, quick, disjointed. It has all the makings of a great spacing move. It's so high because it's probably his most reliable spacing move.
Bair -12% damage is pretty nice, as well as good kill power and great for edgeguarding. Though it easy to miss the finisher hit at times while landing, this move is undeniably great.
DA- I think Dash Attack is very, very good. It doesn't do massive amounts of damage (though 10% maximum isn't bad at all), and neither does it KO. However, it goes past shields and is fairly safe anyway. It also has the tendency to eat a lot of a shield, at least for a Dash Attack. It's the move you'll want to use to quickly pick up a Metal Blade, which makes how safe it is more appreciated. I have also had it clank with projectiles such as Dr. Mario's pills, so its priority is also fairly decent. Just an overall good move, with no real flaw. However, the ending it a little bit laggy, but much like Dtilt this doesn't bother you too much because of the fact it moves. Don't spam it, but make sure you do remember to use it every now and again on their shield because it really can apply pressure.
High Tier:
Dtilt -Goes past shields making it hard to punish, and the close-range hit does 8% which is very decent. The fact it moves makes it unusual. It is a little bit laggy on the ending, which means it isn't completely safe. Unlike the DashAttack, it only hits a shield once, which I think makes it place just under it.
Nair -Very nice for spacing, as well as just throwing out a couple percent every now and then. The close-up hitbox does 4% total, as well as an unfitting amount of knockback. It isn't good for KOing however, as the knockback growth seems to be extremely low. Overall, just very useful for racking up damage. There is never truly a bad time to use this because of how safe it is.
Ftilt -Look to Nair, and then just take away safety points. Same concept, however.
Dthrow -You can get follups from this move at low percents, which makes up for it only doing 4%. At middle percents, you can sometimes get an Uair off it. 4% is low, but for combos/followups it's the one to go to.
Pivot Grab & Dash Grab -Decent range.
Pummel -3% per pummel is very good, though the pummel isn't particularly FAST.
Bthrow -Rock's most damaging throw, at 11%. At really high percents, maybe 150% or so by the edge of the stage it can KO, but it isn't great at that. Its primary use is just to be the high damage throw.
Uair -At 20% max damage, this move is a pretty good way to get damage on an opponent in the air, should you land it. There's only one actual "hit", which is the initial hit which does about 3%. The rest of the damage does not flinch you at all, and you are able to act while caught in the move, though I'm not sure how easy it is to get out of it. Getting the KO isn't reliable but it can potentially kill the opponent if they jump near the ceiling blast zone while caught in the move.
USmash -Not the strongest smash attacks in his arsenal in terms of kill power, range or percent, so what makes it the best? Simply, he can cancel into it from a dash, making it good for reads. The fact it has multiple hits also means that it doesn't have to perfectly catch an opponent, unlike DSmash. It also has a single hit that hits through the lower platforms on battlefield. It has a lot of uses, making it one of his stronger punishing options.
Mid Tier:
Grab -Decent range for a standing grab. Nothing more to add.
Fthrow -It's not the best throw to use, and the fact it does less that Bthrow does make it mostly pointless. However if for some reason you don't want to use Bthrow, for example throwing the opponent off the stage, it's okay.
Jab -It's like Ftilt and Nair, just that you're not moving, which means that it isn't as safe. It can be made safe by transitioning to Nair or Ftilt, but that would be using Nair or Ftilt, as well as walking or jumping. It's just that it's standing makes it not was good as Ftilt and Nair, though there are situations where you would want to be standing still. It's just better to be moving.
Metal Blade - Arguably the best of his B moves (which is nothing to be that proud of), Metal Blade is a mixed bag. On one hand, large opponents may be hit 3 times sometimes, which means they'd take 9% from the blade, very good for a projectile (this mainly happens if they're jumping and you throw it directly upwards). The rest of the time, it'll probably be getting you 6% per blade on average, which honestly is still pretty good. As well as this, the 8 angles it can be thrown is nice to have as well because you can use it to edgeguard, as well as dig it into the ground from lots of other places. Once you pick it up, you can z-drop it for fairly reliable combos off of that. The downsides are that it's fairly slow, it can be used against you and that you can only have one on the screen at a time, which kinda sucks if your opponent picks it up. Anything you can do with it, once they have it, they can do to you (except throw it diagonally). Worth throwing out, but not worth using to the extent Link would use his bombs, for example.
Dair -Aside from the spike, this move has little use. It hits hard, but it's laggy on both startup and ending. Also, you do have to get it JUST right to get the spike. During the startup you seem to do a little bit of a hover, which might be for simply landing the hit. Okay, but only offstage.
Utilt -Despite the fact this move does insane amounts of knockback and damage for a tilt when sweetspotted, it is very risky and kind of hard to land. It's also very laggy on the end. It's nice for punishing an airdodge into the ground, but aside from that keep it fresh - for your own good.
Rush Coil -Although it gets you out of combos, it still isn't amazing in my opinion. While good vertical recovery, it is lacking in the horizontal area, which doesn't help Mega Man's already poor horizontal recovery. The fact it doesn't leave you in freefall and the fact it lets you jump afterwards is nice, but the fact it can sometimes save the opponent by accident isn't that great. I have seen people bounce all over the stage using this move, so that's another good thing, but it isn't particularly useful. It has its benefits, but as a recovery move on its own it's just average. By no means is it bad, though.
Crash Bomb -Good only for mindgames and trying to break shields, the crash bomber is a somewhat risky move overall. It can often end up hurting your shield, or hurting you. You could try to follow it up with a grab if they shield, though you could accidentally take damage yourself. If you want to come close to breaking a shield, use it and if they shield, try to throw a metal blade just as they shield it, and then if they're still in shieldstun try to get a Dash Attack in the mix. Three multi-hitting attacks on one shield hurts.
FSmash -Above average range, but only decent kill power. The fully charged version is enormous in range, and power, making it wonderful for edgeguarding. However, isn't great onstage because it's easy to see coming and again, it doesn't hit that hard. It isn't weak, either.
DSmash -Hits VERY hard, and is his most damaging smash attack. The ENTIRE flame pillar on both sides is a strong hitbox, and it doesn't come out after too long. The downside is that it only does this for a couple of frames; the rest of the frames are obscenely weak and will probably never KO in a million years. It's also really laggy on the ending. It's okay for trying to punish a roll, but should you miss those vital frames it'll hardly do anything and you'll just get a tiny bit of damage off and stale the move.
Uthrow -Uthrow is an okay throw, 7%, low knockback, can try to follow up with Uair. It's just not amazing. Maybe I don't use it enough to see how good it is, I just haven't seen much in it.
Leaf Shield:
Leaf Shield -Have you ever tried to use Plant Barrier in MM6? This move is sort of like that, except it only sometimes protects you from projectiles, and often leads you to death if you use it offstage. Also, avoiding the 3% damage total move is as simple as jumping over it and then punishing us for it. Unlike the MM2 Leaf Shield, you can only throw it horizontally. To its credit, it does block practically anything once thrown, but it's so underwhelming there's almost no point to using it. While it is true that while you are rolling or spot dodging or whatever it's still spinning and it'll do damage while it's around you, it's so miniscule that you'd probably be better off going for a jab.
God Tier:
Final Smash -SUPER FIGHTING ROBOT, MEGA MAN!!