Roserade is pretty good, its typing helps it out with taking on Keldeo, it has access to Sleep Powder, which is nice, it can lay both kinds of Spikes, and it has good power and a usable offensive movepool. It is, however, somewhat frail physically, its typing is a mixed blessing, and Sleep Powder isn't Spore by any means. I'm okay with it being C-Rank, but I feel B-Rank is pushing it a bit. B-Rank
Froslass has the niche of Spikes, Spinblocking, and Speed, and it has options like Destiny Bond and Thunderwave to mess people over, as well as Cursed Body, which can be insanely annoying. That's it, though. It makes for one hell of a shaky spinblocker, seeing as it has rather thin defenses and lacking offenses, meaning that it doesn't inhibit many things from switching in on it. Its defensive typing, put bluntly, sucks, and its ability doesn't help it much when it gets one shotted by many, many things. I'd put it in D-Rank, maaybe a low C-Rank at best. It has a very small niche, but it can be used if you need both hazards and a spin blocker at the same time.
While I'm at it, I'd like to see Toxicroak drop to C-Tier. Toxicroak has two sets you will see, SD and SubPunch, which are both doing the same thing. It has really mediocre stats, and its typing has some interesting resists, but brings a couple huge weaknesses to the table. It can only be used in rain, due to its ability Dry Skin, which is good, but not enough, imo, to make it worth using Croak. It also faces competition from Lucario and Breloom, too, who are usable on a larger number of teams, and have many advantages over Toxicroak. I wanna hear your opinions on it, though. Thoughts?
EDIT: Almost forgot this, Toxicroak is supposed to be able to counter Keldeo with its typing and ability, but...
252 SpA Choice Specs Keldeo Secret Sword vs. 0 HP / 0 Def Toxicroak: 147-174 (47.88 - 56.67%) -- 0.39% chance to 2HKO after weather (rain)
That is one hell of a shaky counter if it can get 2HKOed by a STAB attack. That's ignoring all entry hazards and prior damage, too.