So Leaf Wallop says during your next turn, this Pokémon's Leaf Wallop attack does 40 more damage. So on the first time the Pokémon does Leaf Wallop, it does 40. The next turn it does 40 more so it does 80 damage. Here's my question. On turn three, does it do 120 damage? If not, then how much does it do?
It will be 40,80,80,80,80.
Leaf Wallop does 40 damage the first turn it is used and then 80 damage each turn it is used after that.
Note: Any time Virizion is benched or leaves play (after it uses Leaf Wallop) the effect of Leaf Wallop will end and it will only do 40 damage if used again after that.
Source: Here and here.
Hope I helped :)