Other known variants
x2Wild Growth
As long as Meganium is in play each Grass Energy card attached to your Grass Pokémon instead provides GrassGrass. This power stops working while Meganium is Asleep, Confused, or Paralyzed.
Soothing ScentThe Defending Pokémon is now Asleep.
The aroma that rises from its petals contains a substance that calms aggressive feelings.
If I have Meganium with "Wild Growth" Ability on the bench and Teal Mask Ogrepon with 2 Basic Grass Energy attached in the Active Spot, can I use its "Myriad Leaf Shower" attack if Nighttime Mine Stadium is in play?
Yes, you can. Wild Growth counts the 2 Basic Grass energy cards as 4 energy, so you satisfy the new attack cost of 4 Energy due to the Nighttime Mine.
If I have Meganium with the "Wild Growth" Ability in play, does my Teal Mask Ogerpon ex's "Myriad Leaf Shower" attack do +90 or +180 more damage if there are only 3 basic energy cards attached to it and no energy on the Defending Pokemon?
You get +180 more damage. When an effect counts "attached" energy you count the total amount of energy including the amount added by abilities like Wild Growth.
If I have both Meganium with the "Wild Growth" Ability and Venusaur with the "Jungle Totem" Ability in play, does each Basic Grass energy count as 4 Grass energy?
No. Each Ability is a replacement effect, not an additive effect. So one would replace the other and you would still wind up with each Basic Grass energy providing 2 Grass energy.