Leonard said:-

A sensible version of Clue would be more like the movie. One player would be the killer, whose goal would be to obscure the truth and eliminate the other players from the game, either by causing them to make false accusations, or by killing them as well. […] Players would have reason to form alliances and stick together, and the board would have a real purpose. Still have to do something about the arbitrary accusation rules, though.

Kevan said:-

Ben and I were talking about this a few weeks ago, for reasons I forget, and I don’t think we came up with any solid solution to the “secret murder” problem - it’d be great to have a game where NPCs (or even PCs) could be bumped off in secret, if they ended up alone with the murderer-player, and nobody but the murderer would be aware of it until the body was discovered. […] I think you’d have to include a GM player who’d watch over the game, know who the murderer was, assume that they’d kill at every opportunity, and announce that players are retroactively dead when someone found their body, or (a bit weirdly) when they walked back into an occupied room.

Leonard:-

Now that you’ve brought up the undead, though, here’s a solution to the secret murder problem: anyone murdered becomes a zombie. As long as you can secretly communicate to a player that they’ve been killed, they can keep rolling the dice and staggering aimlessly around until someone else notices that they’re a zombie.

Kevan:-

Aha, solving the wandering-corpse problem with zombies is absolutely perfect. The secret communication could perhaps be a weapon-card thing - give each player a weapon to begin with, and have the rules insist that players secretly flash their weapon cards to anyone they pass in an otherwise empty room. If someone flashes the poison card at you, then you have been zombified by the evil Dr Body.

The zombies either have to attack the detectives (but hold back long enough for them to forget where the zombie came from), or just avoid them for as long as possible; if the detectives are all eliminated before they can unmask Doctor Body, then the zombie team wins. Perhaps with some sort of recognition for the zombie who put the most work in.

Will added:-

OR, decree that only two people may be present in a room at one time. It would work with the whole suggestion aspect of the game. Actually, that works quite well. Then, the killer can’t attack you unless you suggest/suspect him, which gives decent enough motive.

The original Cluedo rules are available online for reference, but I think we’ve thrown most of it out, beyond the board - the whole “Miss Scarlett, in the ballroom, with the lead piping” element is lost, if the weapon is always the same, the location is meaningless and the identity of the murderer is already being tracked by the weapon cards.

(I suppose this means we could use the location and character cards for other purposes. Possibly use the character cards for a facetious combat system; if you’re being attacked by an opponent, or a group of them, draw a card at random from the six, and that’s who gets the punch in. And we could allow the weapon cards to be used as a ‘reroll’, but if your second draw is your opponent, they beat you and get to keep your weapon.)

We haven’t really said how the accusation system would work - given that it’s reduced to just accusing a character, without weapon or location, then maybe it needs a penalty for an incorrect accusation. Perhaps accusations could just be made as straightforward attacks (loser being forced to reveal their weapon card, their identity); if you attack and overcome an innocent, then you’ll be forgiven for being regarded with suspicion.

(Although any mechanic that uncovers a player’s innocence is potentially dangerous, and this goes for the weapon-card rerolls - you could ban players from waving their cards around at whim, but as soon as there’s a mechanic that allows cards to be revealed, it becomes easy enough for the detectives to prove their innocence and isolate the murderer.)