Thank you for the replies, all.
Here is a screenshot of my set up:
As you can see, I have a single orthographic camera facing downward onto a Niagara fluid simulation. I have the camera set to the default for player 0.
When I run the game by pressing the green start button, the player 0 appears below my camera (because I set the camera’s Auto Activate for Player setting to Player 0). I totally want to get rid of player 0, and replace it with my own mesh.
Any help is much appreciated.