Hi I've been laddering with ice, outpeaking all the other ice mains with Ice Stall and I'd like to bring a fresh perspective to ice.
Avalugg: C>A
Avalugg is dead weight surprisingly often, being borderline useless in the Dragon, Fairy, Fire, Ghost, Steel, Normal, Grass, and Sableye Dark matchups due to its inability to do anything to Ghost types. This means it's dead weight against around half the types in the game, this is not a good thing!
Yet Avalugg offers hazard removal and is a fantastic asset in the Fighting and Rock matchups, acting as a solid win condition when the limited amount of special attackers these types have are gone. It also prevents Ice from getting swept by CB scizor. It does this without requiring any support, and should be Ice's default hazard removal option. If you want to climb with Ice, the fighting matchup is super popular and important (and Ice has too many autolosses already); in addition it's ice's only hazard removal option that doesn't require Icy rock support.
Overall an A rank fits this mon the best, showing it's the best default hazard removal option despite its rather serious flaws on a type desperate for hazard removal.
Alola Sandslash: B>C
It's a spinner that attempts not to get spinblocked due to having actual speed and offensive stats; in addition to this it also acts as speed control, which Ice doesn't have many options for. What's not to love?
Unfortunately, it also requires a bit of support to really reach its full potential. It basically forces Ninetails-alola to run Icy rock, nerfing it's screens for the rest of the team. In addition, it's also kind of weak; the dexset of Iron head/eq/knock/spin isn't strong enough to not be setup bait for things like Volcarona, Dragonite, bulky Twave Gholdengo (who also spinblocks it...); in addition, it's not quite fast enough to outspeed things you'd really like such as +2 Ceruledge, +1 Battle Bond Greninja and +2 Iron crown.
Overall this mon is a medicore mon as both a speed control and removal option, and nerfs your screens in order to function. I think C rank is a good place for this; I don't believe this belongs with other B ranks like Froslass and Cloyster, who are more self-sufficient.
Cetitan: A>B
Cetitan is a one-trick pony that also requires a bit of support to really reach its full potential. It basically forces Ninetails-alola to run Icy rock, nerfing it's screens for the rest of the team. It actually requires more support than Snowslash does, as it requires spin support due to running a Sitrus berry instead of HDB; Snowslash tends not to fit on such teams since you don't have enough snow turns for 2 abusers; as such, teams with Cetitan tend to run Avalugg. This means you're running two pure-ice types, which unsurprisingly leads to team synergy issues for a type with as many weaknesses as Ice has.
This issue is compounded when you realize that Cetitan's also best in the flying and dragon MUs, two matchups that Ice should already win by virtue of the type chart. This makes Cetitian effectively a win-more mon that screws over your team synergy in order to function properly.
If anything, I feel that B rank is a bit high for this mon, but I'll settle with B because there is still value in having a strong win condition in the Flying and Dragon MUs as these matchups are far from a guaranteed win for Ice.
Frosmoth: C>D
This is hard to justify. While it's not unviable, it would require some very specific team structures for me to consider adding it; generally Specs Kyurem does whatever QD Frosmoth wants to do better. Defog moth is interesting but again, hard to justify on a type that gets an excellent spinner in Avalugg. D rank is where this fits best I think, alongside other similarly hard to justify mons like Piloswine and Dewgong.
Articuno: C>D
The problem with Articuno is that it takes way too much from it wants to switch into. Look at the calcs:
252 SpA Choice Specs Protean Greninja Sludge Wave vs. 248 HP / 208+ SpD Articuno: 127-150 (33.1 - 39.1%) -- 99.9% chance to 3HKO
252 SpA Choice Specs Flutter Mane Moonblast vs. 248 HP / 208+ SpD Articuno: 153-180 (39.9 - 46.9%) -- guaranteed 3HKO
252 SpA Choice Specs Flutter Mane Power Gem vs. 248 HP / 208+ SpD Articuno: 344-408 (89.8 - 106.5%) -- 37.5% chance to OHKO
4 Atk Iron Valiant Close Combat vs. 248 HP / 0 Def Articuno: 162-192 (42.2 - 50.1%) -- 0.4% chance to 2HKO
252 SpA Expert Belt Iron Valiant Thunderbolt vs. 248 HP / 208+ SpD Articuno: 144-170 (37.5 - 44.3%) -- guaranteed 3HKO
252 SpA Choice Specs Iron Valiant Moonblast vs. 248 HP / 208+ SpD Articuno: 141-166 (36.8 - 43.3%) -- guaranteed 3HKO
252 SpA Life Orb Sheer Force Landorus Focus Blast vs. 248 HP / 208+ SpD Articuno: 130-153 (33.9 - 39.9%) -- guaranteed 3HKO
0- Atk Sheer Force Landorus Rock Slide vs. 248 HP / 0 Def Articuno: 308-364 (80.4 - 95%) -- guaranteed 2HKO
252 SpA Choice Specs Spectrier Shadow Ball vs. 248 HP / 208+ SpD Articuno: 135-160 (35.2 - 41.7%) -- guaranteed 3HKO
These calcs show the kinds of Special attackers you want Articuno to switch into; even if they don't predict the cuno-switch in it's still a 3HKO, which means Articuno is forced to Roost if it wants to be able to switch in again. This gives the opponent a free switch to a potentially very dangerous threat as Articuno doesn't have much offensive presence. And of course, if they do predict the Cuno switch-in with Rock Slide or CC it can easily mean a dead Articuno; in addition, it's also suspectable to Shadow Ball drops from things like Specs Flutter Mane and Specs Spectrier.
Overall hard to justify this mon has it's just not that good of a wall. Belongs in the same rank as stuff like Pilowine IMO.

Avalugg is dead weight surprisingly often, being borderline useless in the Dragon, Fairy, Fire, Ghost, Steel, Normal, Grass, and Sableye Dark matchups due to its inability to do anything to Ghost types. This means it's dead weight against around half the types in the game, this is not a good thing!
Yet Avalugg offers hazard removal and is a fantastic asset in the Fighting and Rock matchups, acting as a solid win condition when the limited amount of special attackers these types have are gone. It also prevents Ice from getting swept by CB scizor. It does this without requiring any support, and should be Ice's default hazard removal option. If you want to climb with Ice, the fighting matchup is super popular and important (and Ice has too many autolosses already); in addition it's ice's only hazard removal option that doesn't require Icy rock support.
Overall an A rank fits this mon the best, showing it's the best default hazard removal option despite its rather serious flaws on a type desperate for hazard removal.

It's a spinner that attempts not to get spinblocked due to having actual speed and offensive stats; in addition to this it also acts as speed control, which Ice doesn't have many options for. What's not to love?
Unfortunately, it also requires a bit of support to really reach its full potential. It basically forces Ninetails-alola to run Icy rock, nerfing it's screens for the rest of the team. In addition, it's also kind of weak; the dexset of Iron head/eq/knock/spin isn't strong enough to not be setup bait for things like Volcarona, Dragonite, bulky Twave Gholdengo (who also spinblocks it...); in addition, it's not quite fast enough to outspeed things you'd really like such as +2 Ceruledge, +1 Battle Bond Greninja and +2 Iron crown.
Overall this mon is a medicore mon as both a speed control and removal option, and nerfs your screens in order to function. I think C rank is a good place for this; I don't believe this belongs with other B ranks like Froslass and Cloyster, who are more self-sufficient.

Cetitan is a one-trick pony that also requires a bit of support to really reach its full potential. It basically forces Ninetails-alola to run Icy rock, nerfing it's screens for the rest of the team. It actually requires more support than Snowslash does, as it requires spin support due to running a Sitrus berry instead of HDB; Snowslash tends not to fit on such teams since you don't have enough snow turns for 2 abusers; as such, teams with Cetitan tend to run Avalugg. This means you're running two pure-ice types, which unsurprisingly leads to team synergy issues for a type with as many weaknesses as Ice has.
This issue is compounded when you realize that Cetitan's also best in the flying and dragon MUs, two matchups that Ice should already win by virtue of the type chart. This makes Cetitian effectively a win-more mon that screws over your team synergy in order to function properly.
If anything, I feel that B rank is a bit high for this mon, but I'll settle with B because there is still value in having a strong win condition in the Flying and Dragon MUs as these matchups are far from a guaranteed win for Ice.

This is hard to justify. While it's not unviable, it would require some very specific team structures for me to consider adding it; generally Specs Kyurem does whatever QD Frosmoth wants to do better. Defog moth is interesting but again, hard to justify on a type that gets an excellent spinner in Avalugg. D rank is where this fits best I think, alongside other similarly hard to justify mons like Piloswine and Dewgong.

The problem with Articuno is that it takes way too much from it wants to switch into. Look at the calcs:
252 SpA Choice Specs Protean Greninja Sludge Wave vs. 248 HP / 208+ SpD Articuno: 127-150 (33.1 - 39.1%) -- 99.9% chance to 3HKO
252 SpA Choice Specs Flutter Mane Moonblast vs. 248 HP / 208+ SpD Articuno: 153-180 (39.9 - 46.9%) -- guaranteed 3HKO
252 SpA Choice Specs Flutter Mane Power Gem vs. 248 HP / 208+ SpD Articuno: 344-408 (89.8 - 106.5%) -- 37.5% chance to OHKO
4 Atk Iron Valiant Close Combat vs. 248 HP / 0 Def Articuno: 162-192 (42.2 - 50.1%) -- 0.4% chance to 2HKO
252 SpA Expert Belt Iron Valiant Thunderbolt vs. 248 HP / 208+ SpD Articuno: 144-170 (37.5 - 44.3%) -- guaranteed 3HKO
252 SpA Choice Specs Iron Valiant Moonblast vs. 248 HP / 208+ SpD Articuno: 141-166 (36.8 - 43.3%) -- guaranteed 3HKO
252 SpA Life Orb Sheer Force Landorus Focus Blast vs. 248 HP / 208+ SpD Articuno: 130-153 (33.9 - 39.9%) -- guaranteed 3HKO
0- Atk Sheer Force Landorus Rock Slide vs. 248 HP / 0 Def Articuno: 308-364 (80.4 - 95%) -- guaranteed 2HKO
252 SpA Choice Specs Spectrier Shadow Ball vs. 248 HP / 208+ SpD Articuno: 135-160 (35.2 - 41.7%) -- guaranteed 3HKO
These calcs show the kinds of Special attackers you want Articuno to switch into; even if they don't predict the cuno-switch in it's still a 3HKO, which means Articuno is forced to Roost if it wants to be able to switch in again. This gives the opponent a free switch to a potentially very dangerous threat as Articuno doesn't have much offensive presence. And of course, if they do predict the Cuno switch-in with Rock Slide or CC it can easily mean a dead Articuno; in addition, it's also suspectable to Shadow Ball drops from things like Specs Flutter Mane and Specs Spectrier.
Overall hard to justify this mon has it's just not that good of a wall. Belongs in the same rank as stuff like Pilowine IMO.