Nominating Crustle and Omastar for C-Rank and Ferroseed for D-Rank.
These three Pokemon all have a niche of having both Stealth Rock and Spikes.
Crustle can Custap Lead to serve as a weaker Deoxys-D guaranteeing two hazards and can fight back with 95 Attack, and 125 Defense is decent. It has some flaws in bad defensive typing and a weak 75 SDef. C-Rank for me.
Omastar is a different Spiker. It can burn with Scald and has Ice Beam for coverage, coupled with a decent 115 SAtk. It can also Shell Smash to try to sweep, though Zapdos, Raikou, and Mienshao can KO it before it sets up thanks to poor Speed. C-Rank for me.
Ferroseed. It is much harder to do its job with Xatu around than in RU, but it can wall any Choice-locked Poison-type attack and use it as setup fodder. It is outclassed in the bulk department by Cofagrigus, Gligar, Slowbro, and even Hitmontop, and it is Taunt bait, and bulky Grass-types wall it, but it can set up Spikes unlike the other four. D-Rank for me.
I second these notions, since these three are unique in the sense that they can set up both Spikes and Stealth Rock, and are great as suicide leads in general.
I'd like to nominate Scolipede for
C-Rank, because he has an awesome Speed tier, outpacing Froslass and Tornadus, while he has Spikes to back up his Speed, making him an awesome asset to offensive teams. While he faces much competition from Froslass and Accelgor, Scolipede hits notably harder than both, putting the extra hurt with Megahorn, and if his Sash activates, he can fire a Swarm powered Megahorn to hit hard. He is also not completely helpless against Nidoqueen and Nidoking thanks to Earthquake / Aqua Tail, unlike Accelgor. Scolipede has access to Swords Dance, allowing him to serve as a great physical sweeper and can use his awesome physical movepool, with Megahorn as well as options in EQ, Rock Slide, Aqua Tail, and Poison Jab to hit mighty hard, and stands out from Heracross with his greater Speed tier.
Accelgor imo is definitely
C-Rank, since like Scolipede, he is an excellent speedy spiker, outpacing practically the entire UU metagame while setting up Spikes in their faces, and has a nice Special Attack and Bug Buzz, Focus Blast, and HP Rock or Giga Drain to lay the hurt, much like his centipede cousin. He has Final Gambit so if they don't do anything while he Spikes, he can sacrifice himself to deal some good damage to the opposing team. He can also run an offensive set, with Life Orb and the four aforementioned attacks, putting quite a bit of hurt on the team.
On the hail discussion, I could support moving Rotom-F and Walrein up; since hail is the only auto weather and the two are extremely lethal in the hail.