@FlutterLove
The thing meganium needs most to be usable is a better movepool imo, it has
extremely few usable attack options, heck your set has the ENTIRETY of it’s usable physical moves and you aren’t even running a full four attacks! I would say give it something like a steel, fairy , rock or maybe ground typing and thick fat or regenerator with a more bulky spread like say,
122atck 120def 70spatck 120spdef 110spd.
The biggest problem with meganium is that it’s a grass type, which is by far the worst type for both offense and defense, and dragon may help a bit, but sharing a weakness to ice and ineffectiveness against steel is crippling.