I really should have posted this before Ryota finished his/her/their/its run with a Torterra. Better late than never, I guess. Anyways, this is what happened when I used a Torterra a few months ago.
Now that at least 3 people have used Torterra and say it should be B tier, I think it's time to read Drumstick's, Moonlight's, and Ryota's logs and attempt to figure out why we got such different results.
Gardenia: I was able to get more consistent sweeps because I used return instead of bite. Because Gardenia's Turtwig wastes so many turns using reflect and sunny day, it's pretty easy to set up 4 to 6 curses and 2HKO her Turtwig before Grotle loses half of its HP. Additionally, giving Grotle an Oran berry lowers the chance of needing a super potion.
Jupiter: This is where return really matters. While her Skuntank resists both razor leaf and bite, Grotle's +2 return 3HKOs Skuntank. Zubat's wing attack is super effective, but it is still too weak to stop Grotle from setting up and sweeping.
Fantina: Rawst berry allows Grotle to set up on her Duskull. Yes her Mismagius can use confuse ray. Yes Grotle still needs luck to sweep. However, most other A tier things can just barely touch her Mismagius regardless of how lucky they get, so I still consider this a relatively good matchup for Grotle.
Rival (209): Even though wing attack is super effective, his Staravia still uses 2 or 3 double teams before attacking. Grotle can easily use curse during these turns, and wing attack is no longer a threat when Staravia actually starts using it. Grotle can continue cursing until return is a guaranteed OHKO, so endeavor isn't a problem either. Even if a teammate needs return more than Grotle does, Grotle can use secret power, which is still an upgrade over bite and also neutrally effective against Monferno.
Rival (Pastoria): Again, Torterra can use return to defeat Staravia without losing much of its own HP.
Wake: A Sitrus berry lets Torterra survive one ice fang from Floatzel, OHKO Floatzel with wood hammer, and survive the recoil. Of course, Torterra can then easily take out Quagsire. Similarly to Fantina, Wake is a difficult opponent even for A tier Pokemon. Being able to consistently defeat 2 of his Pokemon, including Floatzel, is a very strong performance.
Volkner: You don't need rock polish to sweep this one. Jolteon effectively can't touch Torterra, so Torterra can easily set up 6 curses and use synthesis to heal the tiny bit of damage from iron tail. Raichu gets to use one signal beam before earthquake OHKOs it. At +5 or +6 physical defense, Volkner's 2 physical attackers can't do much, so Torterra can heal itself again and continue sweeping.
Rival (League): Torterra can't solo, but it can still use curse and synthesis to defeat both Staraptor and Heracross.
Bertha: Whiscash is easy setup bait. Even when sandstorm is making synthesis less effective, it is still more than enough to heal all the damage that Bertha can do to a Torterra with +6 physical defense. Wood hammer recoil isn't an issue because earthquake OHKOs everything except Gliscor.
Flint: Torterra needs rock polish to completely sweep but can take out 3 Pokemon without rock polish.
Lucian: Bronzong does not force Torterra to switch out if Torterra uses swords dance, as +2 wood hammer is a 2HKO. Torterra outspeeds Bronzong and can use synthesis after taking some recoil from the first wood hammer. After Bronzong, Torterra can defeat either Alakazam or Gallade. It's not a solo, but taking out 4 of his Pokemon is still pretty good.
Although there were a bunch of things I did differently with my Torterra, return and synthesis are definitely the most important. Return makes Torterra better at sweeping Gardenia and a few rival battles and completely turns the tables against Jupiter, while synthesis lets Torterra very reliably solo Volkner and Bertha and also heal a lot of damage in the last rival battle and against Lucian. With synthesis, the second half of the game is not nearly as bad as Drumstick described it.
Another issue that all of Drumstick, Moonlight, and Ryota mentioned is 4MSS. According to my logs, this sequence of moves is already enough to sweep many of the major battles.
razor leaf -> wood hammer
bite -> earthquake
curse
return -> synthesis
There are only 3 times when Torterra really wants another move: Aaron (swords dance and stone edge), Flint (rock polish), and Lucian (either swords dance or rock polish). You could still argue that Torterra has the worse 4MSS compared to the A tier things that people aren't trying to drop, but they have other minor issues that Torterra doesn't have. Being affected by 4MSS in 3 battles just doesn't seem like a very big problem.
I hope this post was enough to show what I did differently and how that caused a stronger and more consistent performance from my Torterra. So what do you think? Are these valid strategies that Drumstick, Moonlight, and Ryota overlooked, or did I set my standards too low?
Additionally, there are some other recently proposed updates that were almost completely ignored. Is Ikazuchi going to make these updates or no?
Magnemite from C to B
Croagunk from D to C
Wurmple (Dustox) from E to D
Buneary from D to C
Nosepass from E to C
Rotom from C to B