Shadow Torterra

Shadow Torterra trails behind Shadow Venusaur in performance, but still performs decently well with slightly better bulk. A Grass/Ground typing means Shadow Torterra does not have a resistance to Water-type attacks unlike other Grass-types, which could cause it to faint sooner than expected. Its 2x weakness to Ice-type attacks should be noted, as many Water-types carry Ice-type moves, though a 3x resistance to Electric-type attacks can be appealing in very specific situations. 

Best PvE Offensive Moveset

• Razor Leaf + Frenzy Plant makes Torterra a formidable Grass-type.

• Solar Beam can be used if you don't have access to the Community Day exclusive move, though it's much worse.

• Earthquake has STAB; it’s usable with Razor Leaf, or Bite if Grass is resisted.

• Without STAB, there aren’t any edge cases where Stone Edge should be used.

• Sand Tomb has very poor damage output for PvE. 

Best PvE Defensive Moveset

• Razor Leaf has much more power than Bite, and STAB to boot.

• With its other moves all being 1-bar charged moves, Frenzy Plant can at least damage some Pokemon before it dies.

• Of the remaining moves, a surprise Stone Edge is nice coverage.

• Solar Beam and Earthquake, though stronger, are far too easy to dodge.

• Sand Tomb can be used frequently as a 3-bar move, though it's not hard to dodge. 

Razor Leaf takes advantage of STAB to deal massive damage, at the cost of the offering the worst energy generation in the game. Bite is generally an inferior move due to a lack of STAB and also worse damage output stat-wise, but an off-typing can catch opponents by surprise in certain formats. 

Frenzy Plant is very powerful and hits even harder with STAB, but is somewhat redundant due to the high damage output of Razor Leaf. Sand Tomb is recommended to for its low energy cost and debuff utility. Stone Edge is good for coverage against all of Torterra's weaknesses, though poor energy gains makes it difficult to use. Earthquake benefits from STAB and provides wide coverage against numerous typings, but 65 energy is a lot to ask for from Torterra.