Note: you can do this on either on forge or custom games, I do this on custom games because it makes the game more fun.
First, set up any map that you choose, a big one works better. Then when your back to the page where you start the custom or forge game, press X and then go down to "general settings" and then click on the "base player traits".
Go to "Movement" and change the player speed to 300% and the player gravity to 50%, then go back to the start page and start the game.
And have fun jumping around like flood and running faster than a mongoose!