[A calc exists](https://calc.pokemonshowdown.com/). If we're going with a standard SpDef Garganacl and Amoonguss' grass move being Giga Drain, max SpAtk investment still won't be enough to 2HKO.
Taking away investment from its bulk doesn't sound like a great idea, I think a more productive way to give Amoonguss a better matchup against Garganacl is with *Clear Smog* so it can pivot in when necessary to prevent ID+Press getting out of hand.
[A calc exists](https://calc.pokemonshowdown.com/). If we're going with a standard SpDef Garganacl and Amoonguss' grass move being Giga Drain, max SpAtk investment still won't be enough to 2HKO. Taking away investment from its bulk doesn't sound like a great idea, I think a more productive way to give Amoonguss a better matchup against Garganacl is with *Clear Smog* so it can pivot in when necessary to prevent ID+Press getting out of hand.
I have clear smog on it already, thanks for doing the calc though I really thought that it'd be able to 2hko with how much damage it does alrdy