ok. Time to change this.
Dusknoir is a crappy Pokemon that should be in the Munchlax level. It has no recovery, isn't the best spin-blocker, is pretty weak offensively if you invest in defenses which you need to because otherwise it sucks even more, it can't do anything to any Pokemon outside of burn it, which is a complete joke. To run random stuff like Fire Punch you're just taking up moveslots. Dusknoir can only run 4 moves, and Pain Split / Shadow Sneak / Will-O-Wisp are non-negotiable, as otherwise it is complete set-up fodder. That leaves one slot for Fire Punch / EQ / whatever random move you feel like running there, and that just means you will be raped by every other Pokemon that that move doesn't hit. Pokemon with Substitute, and hell, even Zangoose can set up an SD on this piece of shit Pokemon and own a weakened Dusknoir with Night Slash. Weakening Dusknoir is ridiculously easy since it is susceptible to status and entry hazards, not to mention Pain Split can be easily played around by sending a Pokemon that is low on HP into Dusknoir, or just using Substitute. Awful Pokemon, move it to E Rank kthx.
1. Comparing Dusknoir to Munchlax seems unfair. Noir can run Leftovers, Munchlax can't (it desperately needs Eviolite to do anything). Dusknoir has a base 100 Atk stat, Munchlax has base 85 and doesn't sport the defenses necessary to make use of much, even with Eviolite. Munchlax can't even burn things, much less do other kinds of status.
You also contradict yourself when you say Noir has no recovery. It has Leftovers and you mandate Pain Split. Pain Split was enough to differentiate Noir from Cofag back in BW1. It also has Rest, which other Ghosts have. I'm not saying Noir is S Rank by any means (I did say B Rank tops, and would be amenable to demoting Noir to C Rank myself), but it's not awful enough to be in E Rank.
2. Dusknoir is in B Rank because, like you said, it isn't the best spinblocker (do mind that the other good spinblockers, Spiritomb and Rotom-N, are firmly A-Rank Pokemon; I'd personally argue Rotom-N to go higher to S Rank, even). It's still a spinblocker, which means it still has a good niche keeping it from going to E Rank. As mentioned earlier, there are less Ghosts in the tier than there were back in the AlakaSableye era. Noir has a key niche as a Cryogonal counter shared exclusively with Spiritomb, who is A Rank. As mentioned earlier, as a Cryo counter it only partially competes with Tomb. It's not completely outclassed by all spinblockers, or I would propose C Rank instead.
3. Fire Punch isn't random. It still allows Noir to hit Cryo hard while also hitting Escavalier and other Pokemon hard as well. If Fire Punch does not suit your needs, you can also run ThunderPunch or IcePunch, or something else which suits your fancy. I run a SubPunch set which is effective. It's not spectacular, but it's effective.
4. Dusknoir is in B Rank
because stuff can still set up on it, but it can still hit back relatively hard and it can still take hits decently. Did you read the annotations on each rank in its detail at all?
5. Ghost-types in general aren't too particular to status and hazards. It's not like any of them, say, have a Steel-type which makes them immune to poison. Of the three Ghost-types in RU, Rotom-N is the only one to avoid Spikes and Toxic Spikes due to Levitate. Not even Cofagrigus could boast that. Are you going to argue Spiritomb be dropped to D Rank because its movepool and susceptibility to hazards don't make the cut, too?
6. Zangoose could set up on Ghost-types in general, even its supposed "check" Haunter. It's not just Dusknoir. Why do you think Zangoose was almost banned to BL3 when it was Suspected?
7. Tomb and Rotom-N also use Pain Split. That the move is inconsistent is what keeps them from being S Rank, and what keeps Noir from joining them in A Rank. Unless an influx of Ghost-types show up to RU's doorstep looking to replace Noir, it still has an anti-Cyro niche which keeps it firmly in B/C Ranks. E Rank would mean that there are more than enough Ghost-types in use to make RapidSpinners' lives a living hell. So far, I only see three, with possibilities of a fourth Ghost in Golurk, who runs Drain Punch and does other stuff entirely such it couldn't really outclass Dusknoir as a defensive Pokemon (although as a physical Attacker that's different, albeit because of Drain Punch making it more effective in recovery).
8. For a Pokemon to be E Rank, they have to be ineffective at
everything they do, and have stats so average/inadequate that they cannot distinguish themselves from others better than them. A base 100 Attack (shared by fellow Pokemon Tangrowth and Klinklang, who I also view as better than Dusknoir mind) along with the currently best base Special Defense (135) and third best base Defense (135) means it's not going to E Rank on my watch. However, second-worst base HP (45) does make it not A Rank potential ever (and this is something I agree with), as does being partially outclassed (not completely, mind) by Spiritomb in other venues not related to Cryo at all (and by Rotom-N at least when it comes to Kabutops). Its base Speed is better than Spiritomb's, but that means it's a slightly less effective Trick Room setter (which Tomb doesn't even do, last I checked).
I'd rather send every NFE other than Scyther to E Rank before I send Dusknoir anywhere near D or E Ranks.
9. The lowest I'm willing to drop Dusknoir down to is C Rank. There are people who argue Ambipom's usefulness in UU such that it is C Rank in that tier, whilst I genuinely believe it is E Rank there. However, just because a Pokemon is outclassed does not mean it is bad in general (that's legit the words the first person who argued against my proposal of sending Ambipom to E Rank said). It still has uses, albeit tenuous ones with weaknesses keeping it from being in A Rank (mono-Ghost isn't doing Noir any favors, and neither is sharing a two-Pokemon niche in being a Cryo counter).
10. I'm also using Dusknoir as a Rain Dance setter on a different team. Because it is so bulky, it can pull this off rather nicely. However, even I know there are a few other arguably better Rain Dance setters in the tier (Volbeat, to name one). Rain Dance isn't going to make Noir A Rank either.
You would have to make
every niche Noir has impossible to do if you want Noir to be D Rank (as I can still argue its superiority to Ferroseed and Munchlax all day). Which in of itself is impossible as there are so few Ghost-types in RU that C Rank is the lowest Dusknoir can go without there being some inherent bias against it. And the point of the Ranks is to evade bias. I'm willing to drop it to C Rank to meet this standard if others are willing to agree. Molk and Double01 did when the original list was made.
I deliberately placed it in B Rank instead of C Rank to spark opposition, since in my previous argument there had been none. Looks like my plan worked.
The Only Change I Shall Do For Today,
Since It Was Going To Happen Anyway
*Moved Dusknoir down from B Rank to C Rank.