It's very simple, so I'll get right to it

1) Start with your controller unplugged and get to the position selection screen.

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2) Use the arrow keys and Z to select a position to play.

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3) Click the "Start Match" button then plug in your controller.

When I saw the add/remove player button at the top right of the character selection screen, I assumed it would let me remove any player I wanted. However, it seems like this is only used for when you want to play with two people on one keyboard. With a controller plugged in, the button does nothing. But without one, it will allow you to add or remove Player1, and the controls become:

Player0

Player1

I don't know what Player0's controls become on keyboards without a number pad, but if anyone can find that out please let me know and I'll add it to the guide.

I was pretty frustrated about the confusing settings and not being able to replay the story missions with a controller, which was the only negative I could find with this game. Then I stumbled across this stuff by chance and trial and error, so I hope it helps you out,