Pielorinho
Iron Fist of Pelor
I agree with Sammael's advice, for the most part. As the DM, you shouldn't make changes to PC rules without giving them advance notice. However, you're perfectly free to invent new spells, monsters, and magic items, and to change a module beyond all recognition.
In this case, you would have been well within your rights to decide that the wererat that bit the PC was a new monster of your own invention whose disease worked in a different fashion. When a player has the amazing gall to tell you how a monster works, whether or not you've changed the monster from the MM, the correct response is to look at the player blankly and say, "Excuse me?" Make it clear that their PC may persist in denying the monster's behavior, but that doing so indicates that the PC has lapsed into a hallucinatory fugue -- you as the DM have described accurately how the monster is acting, and PCs ignore it at their peril.
You had no duty to tell the player how lycanthropy worked ahead of time. Here's how it would have played out IMC:
Ratguy: When I change, I go down to the temple and attack the priestess.
Me: Okay. Anyone want to do anything before nightfall?
Everyone: Nope (or "I do this random stuff which we resolve quickly.")
Me: The sun sets, the moon rises, I give a little bit of scene-setting detail (the smell of the barn they're in, the calling of owls, or whatever). You, you, and you (no, not you, Mr. soon-to-be-a-wererat), roll spot checks. Those of you who rolled 15 or better see a horrible transformation take place: your evil companion, the one who was rolling around in wererat guts last week, is sprouting fur! growing whiskers! His nose is elongating! His fingernails harden into claws! He begins to shrink! Within moments, a rat the size and appearance of an ungroomed Shih Tzu crouches before you -- and then it leaps, squeaking and frothing, at your throat, Mr. Wizard! Everyone roll for initiative.
Ratguy: No! I told you, I go attack the priestess!
Me: Actually, all conscious thought has fled your mind, and you're filled with an overwhelming rage at all life around you. I'm gonna play your PC for now; I'll let you know when you regain control. [If I trusted you, I'd let you play the rat as an insane creature who attacks whoever's closest to him, but I don't trust you to follow those guidelines].
Ratguy: This sucks!
Me: We'll discuss the rules aspect of it after the session, if you want. What did everyone roll for initiative?
Ratguy: You're a crappy DM!
Me: You need to leave the room if you can't keep quiet. There's a battle to run here.
Note that you don't need to pull out the description of lycanthropy here: the disease's parameters are in the MM, a DM sourcebook and subject to DM change. Unless a PC is a world expert on lycanthropy, he wouldn't know the disease's exact parameters; even an expert on it wouldn't know whether he was infected with standard lycanthropy or some strange variant.
It's your world they've chosen to play in. You get to design it. They get to play their PCs, unless some other force in the world takes over the PC's will. In this case, a force has done so.
It sounds to me like you're right to get rid of that guy. If there are other players in the group who are decent, worthwhile players, you may want to go to them individually and apologize for your outburst, ask them if they'd like to set up a new group, and be willing to work with you.
Good luck!
Daniel
In this case, you would have been well within your rights to decide that the wererat that bit the PC was a new monster of your own invention whose disease worked in a different fashion. When a player has the amazing gall to tell you how a monster works, whether or not you've changed the monster from the MM, the correct response is to look at the player blankly and say, "Excuse me?" Make it clear that their PC may persist in denying the monster's behavior, but that doing so indicates that the PC has lapsed into a hallucinatory fugue -- you as the DM have described accurately how the monster is acting, and PCs ignore it at their peril.
You had no duty to tell the player how lycanthropy worked ahead of time. Here's how it would have played out IMC:
Ratguy: When I change, I go down to the temple and attack the priestess.
Me: Okay. Anyone want to do anything before nightfall?
Everyone: Nope (or "I do this random stuff which we resolve quickly.")
Me: The sun sets, the moon rises, I give a little bit of scene-setting detail (the smell of the barn they're in, the calling of owls, or whatever). You, you, and you (no, not you, Mr. soon-to-be-a-wererat), roll spot checks. Those of you who rolled 15 or better see a horrible transformation take place: your evil companion, the one who was rolling around in wererat guts last week, is sprouting fur! growing whiskers! His nose is elongating! His fingernails harden into claws! He begins to shrink! Within moments, a rat the size and appearance of an ungroomed Shih Tzu crouches before you -- and then it leaps, squeaking and frothing, at your throat, Mr. Wizard! Everyone roll for initiative.
Ratguy: No! I told you, I go attack the priestess!
Me: Actually, all conscious thought has fled your mind, and you're filled with an overwhelming rage at all life around you. I'm gonna play your PC for now; I'll let you know when you regain control. [If I trusted you, I'd let you play the rat as an insane creature who attacks whoever's closest to him, but I don't trust you to follow those guidelines].
Ratguy: This sucks!
Me: We'll discuss the rules aspect of it after the session, if you want. What did everyone roll for initiative?
Ratguy: You're a crappy DM!
Me: You need to leave the room if you can't keep quiet. There's a battle to run here.
Note that you don't need to pull out the description of lycanthropy here: the disease's parameters are in the MM, a DM sourcebook and subject to DM change. Unless a PC is a world expert on lycanthropy, he wouldn't know the disease's exact parameters; even an expert on it wouldn't know whether he was infected with standard lycanthropy or some strange variant.
It's your world they've chosen to play in. You get to design it. They get to play their PCs, unless some other force in the world takes over the PC's will. In this case, a force has done so.
It sounds to me like you're right to get rid of that guy. If there are other players in the group who are decent, worthwhile players, you may want to go to them individually and apologize for your outburst, ask them if they'd like to set up a new group, and be willing to work with you.
Good luck!
Daniel
. But you made the right decision, of course.
