Bold and beautifulG 20

Can be done easily in Free Mode. Start a game with initial capital set to 3 million and make sure you have a few competitors. Other settings don’t matter but I set the pause mode to manual so I could pause.

Go into the Company section of the actions menu and tab over to Competitors. Pick a competitor and buy over 2.5 million of their stock. Select them again and sell it back. Then go over to another competitor and buy over 2.5 million of their stock. Wait a moment and the achievement should pop.