Press on the overheat button to do fast attack When you click enough 10 clicks, you can do a charge attack by clicking on the Use Charge Attack Button. If you want other version of this game, such as: (eg Lucario vs Gigantamax Butterfree) comment down bellow. I'm also adding new buttons such as: Mega, Dynamax, Gigantamax, Z to the game. It will be better, surely.
Strategy I use: Click until the Machamp have 250HP left. And then spam Charge Attack (Don't use Charge Attack before the Machamp reach 250HP left) Credits to Pokemon. And Scratch