I run multiplayer experiments and the only way to review them is to have multiple people be added as collaborator and each logging in simultaneously. It would be useful if there was a way to split the screen during preview with each section be a player. Alternatively, it would be useful to allow the same person log in to the account from more than twice. Right now it is very hard to test multiplayer experiments and it's even more important to test such experiments before recruiting a large group of participants for a session.