Anyway. New campaign. New characters. New possibilities.
I'm trying something different this time. I've been running games of one stripe or another for these players for at least 15 years now, so we all know each other pretty well, and I'm taking full advantage of that. I have two players, who each play two PCs at once. I fill out the standard five-member party with an NPC. The last NPC wound up married and having children with a PC. This time, we've got the same basic setup: two players, four PCs, and the fifth member of the party is my NPC.
This time, however, the NPC is evil, and a plant, and intends to betray them all.
I have never done anything like this before, which is both good (it will be wholly unexpected) and bad (I'm not 100% sure it will be as awesome to them as I hope it will be). And I'm trying to be as fair as I possibly can about it without tipping my hand entirely.
The situation: I'm running the Scales of War adventure path, which is a series of modules published in Dungeon magazine that takes characters from 1st through to 30th level. It centers mostly around the conflict between Tiamat and Bahamut, although that isn't obvious until later. The NPC in question is a dragonborn cleric/barbarian. He is evil, he is a follower of Tiamat, he doesn't quite know exactly why he's been told to hang out with these people, but he's doing so. He knows enough to keep his true beliefs a secret.
I built the NPC with the same rules the players used for their PCs. I made sure that the NPC's Bluff skill was higher than any PC's Insight skill. I used his first Feat for Skill Focus (Bluff), and his first Utility skill was Serpent's Tongue (allows a +5 bonus to the first Bluff check after a Bluff failure).
I never said the NPC was a cleric of Bahamut, either as a GM or as the NPC, but I have absolutely allowed the players to assume he is one, and never corrected them when they call him one. Every time I refer to the NPC's god (either in my voice or his), I use the words "patron" or "deity" rather than a name or even "god" or "goddess". Whenever the NPC mentions either deity by name, I make sure he mentions the other equally (i.e. he was talking about the draconic races being unsubtle -- if Bahamut is pleased with you, you'll know; if Tiamat wants you to do something, she'll tell you. They're not the types to send cryptic dreams or symbolic visions. They, and their messengers, will just up and say what they mean).
The NPC also has a very bad temper, the triggers of which are very Tiamat-like. He doesn't like anyone touching his stuff, and he can't stand to be insulted or disrespected. These will make him lose his temper.
I have also had him insist on splitting the party treasure after every adventure, something I've never had any other NPC do; the players are usually very socialist when it comes to treasure. They tend to keep it in one big pile (well, Bag of Holding) and everyone takes from it as they need to. He claims it's because he has tithes to make with his share, which is at least partially true. The main reason, though, is that he's greedy and doesn't want to share.
I also plan to use every other Feat he gains to give him another type of breath weapon, until he has all five that Tiamat does (fire, lightning, cold, poison, acid). He'll get the fifth one at 16th level. He also carries a portion of his shell with him in a leather pouch that hangs around his neck. He keeps it, because the colours on that shell swirl and look like Tiamat's symbol. His father took it as a sign, and that's how he came to the worship of Tiamat.
He has not had to outright lie yet, but I have a sheet with all the PC's passive Insight scores, and I've rolled the NPC's Bluff score, in advance, around ten times. I've printed the results out on small cards and if he needs to lie to one of them, I'll pick a random card, consult their passive Insights, and go from there. I don't want to tip them off with dice-rolling if I can avoid it. If they get suspicious, I'll of course call for active Insight checks, and things might unravel (hopefully with his Serpent's Tongue power, I'll be able to talk his way out of any grevious failure). But we'll see. I'm prepared for the fact that he might fail completley and be ousted early. I'm good with that. I hope it won't happen, but I'm okay with it if it does.
I'm trying very hard to walk the line between "too subtle to notice" and "swinging the +10 Clue-by-four of Hint-Dropping".
I guess the questions are: am I being fair? Do you think planting a trusted NPC in a party who will eventually betray them all is a betrayal of the players' trust as well? If your GM did this in your game, would you be pissed?
And if not, do you think I'm playing fair with the clues? Too few? Too many? I find it hard to judge.