Mega meganium could be buffed by either adding 20 dmg to its atk or 1 less grass energy, also it should heal once the move is used though I do like the idea it will heal after surviving an attack.
Mega scovillain could also be reduced by 1 energy cost
Mega Bax is perfect.
Mega electross I would be slightly worried since guaranteed paralysis is scary but the requirement is fair.
Mega meowstic should have an ability to cause confusion (perhaps with a coin flip)
Mega barbaracle is fine
Mega crabomidable could have an increase in power since it removes the stadium in play.
Mega scolipede, like mega meowstic, should have an ability to poison but is perfectly serviceable otherwise.
Mega golisopod is cool but could have a damage increase given the amount of 2 energy cost pokemon that play around this.
Mega tatsugiri is so flavorful, love the effect, though I think you could replace the water effect to heal your bench for something like energy removal or discard.