I agree with Toxicroak being S or at least A+. But anyways, just wanted to remind everyone to check the previous posts before you post, in case you are suggesting a rank for a Pokemon that has already been suggested.
Alright, time to complete the Sinnoh Starter Trio with, everyone's favorite Continent Pokemon, Torterra!
Torterra for A- Rank!
Torterra is one of the best Starter Pokemon, with a great Attack and Defense as well as decent HP and Special Defense. It also gains nice moves like Wood Hammer, Earthquake, Crunch, Leech Seed, Synthesis, Curse (Torterra's Speed isn't good anyways), and Seed Bomb (breed). These moves, however, mostly come in Torterra's Level 30s. Still, this Pokemon can do some damage to Keta (but not to Venam). Afterwards, everything is easy, as STAB Earthquake and Leech Seed/Synthesis to live longer is amazing. It can do plenty of damage to Marianette, be a beast for Narcissa with Bite or Earthquake, Razor Leaf away Valerie (sadly, Wood Hammer is relearner only), and hurt Angie intensely if it lives an Ice type move.