You and David are close friends, and do everything together.
You are a very intense person, and do nothing in half measures.
For some time you have been harbouring a hatred of Vanessa and Richard, who spurned you when they were looking for someone to flat with them. Despite you asking first, they asked David to live with them. You have not overlooked David's betrayal either - he will realise his error when he discovers the lie you told him (see below) - but you've kept quiet about that. He does know about your desire for revenge on the others.
You and David have devised a plan to get what each of you wants. By performing a magic ritual during the play, you will cause everything that happens to the characters happen to the actors also. One thing you have kept from David: he believes that what happens to the actors is only a pale echo of what happens to the characters, so no one will die. This is not true (and doesn't bother you). You must play a character who is not harmed in the play, which means being the Monarch and Jester. Given everyone else's fate, this is the only option.
David's only interest is Charlotte, whom he has been enamoured with (as everyone else must be aware) for years, without Charlotte being interested.
At some point in the play, when you and David are on stage together, you must perform the ritual that will make what happens to the characters happen to the actors from that point on. You must each tell the other, in character, that you are creating this effect and that you are free from the results of the spell (this isn't guaranteed, hence your choice of character). This must be done as subtly as possible, because if the other actors learn that this is the case, the spell will no longer affect them as much.