I'm gonna go ahead and throw out a post concerning Cacnea, because it's something that hasn't been covered yet and it's interesting to theorymon about Pokemon that aren't viable.
The main thing that Cacnea has in its arsenal is Water Absorb. It's a very nice ability that allows you to punish Scalds, Surfs, and Hydro Pumps on switches, as well as completely wall Pokemon that may be Choice-locked into a Water-type move. Plus, I feel like the niche of being a Grass-type with Water Absorb gives it a place in Sun teams, since it has good mixed attacking stats and STAB Solarbeam, and it can switch into a lot of Vulpix's and Ponyta's threats. Being able to resist Ground and Electric is also a big plus.
Cacnea has a pretty diverse movepool, and has some unique moves in LC. It has access to a lot of different support moves:
-Switcheroo, which can possibly enable a Scarf set (since it can get to 14 Speed)
-Spikes, which allows it to set up hazards against Water-types that it walls
-Synthesis for recovery.
-Destiny Bond, though it's too slow to abuse it correctly.
Plus, its coverage is pretty potent, with moves like Drain Punch for Darks and Steels, STAB Bullet Seed (Sturdy breaker, with 100% accuracy)/ Seed Bomb (strong physical Grass STAB)/ Solarbeam (for aforementioned use in Sun teams), Poison Jab for fairies, and priority with Sucker Punch.
Problem is, Cacnea is horribly slow and is cursed with terrible bulk. Plus, while it has a large movepool, not many of those moves are very impactful, and it can't get Knock Off, which is a big disappointment. That being said, I think it can have a small niche in certain Sun teams. It's no Bellsprout, but having Water Absorb really gives it something to work with. I think it could easily go up to C, but I don't think it should go any higher. I don't think it belongs in the same tier as Oddish, which it clearly outclasses utility-wise, even without Chlorophyll.
However, most of this is theorymon and largely untested and/or complete. What do you guys think?