Question

What are all of the Pokémon that can Mega-Evolve AND can Gigantamax?

Answer 1

Venusaur
Charizard
Blastoise
Gengar

That's all of them. None can Mega Evolve and Gigantamax in the same generation, however.

Source

Hope I helped!

Answer 2

• Blastoise
• Charizard
• Gengar
• Venusaur

Source: Pokemon Showdown teambuilder

Hope this helps!