Meganium is one of my most favorite grass-type Pokémon. It looks extremely cute to me, and its smile always bring sunshine on a cloudy day. :) Meganium is the strongest Pokémon defensively out of the three starters of Johto. With access to moves such as Aromatherapy, Toxic, Dragon Tail, and Synthesis, it's able to take on the role of a supporting Pokémon without any worries. Toxic allows it to inflict the opponent with poison which steals their health bit by bit on every turn. Aromatherapy can heal the status effects of all of your team members, eliminating the need for Antidotes, Burn Heals, Ice Heals, and other healing items. Dragon Tail can make your opponent's Pokémon switch forcefully and get themselves hurt with entry hazards. And finally, Synthesis allows it to recover itself whenever it's low in HP.
Thiere are plenty of other useful moves that this Pokémon can learn, but right now, these are the only ones that I can think of from the top of my head. d: