There is no limit on how many vehicles can participate in the game, but it needs to have at least 7 players and a moderator. The moderator is called the "Matchmaker" and observes the game as well as makes the final decisions. The roles are assigned to the vehicles in private via a radio message at the beginning of the game, by the Matchmaker. Two vehicles are assigned the role of the "Hellcats". Their objective in the game is to "kill" all the other players without being revealed and killed themselves. If there are many participants, additional Hellcats may be appointed. One vehicle is assigned the role of the "Scout". They can try to find out about the Hellcats' identities and warn the others, but should not reveal themselves since the Hellcats might try to kill them immediately if they do. One vehicle is assigned the role of the "Mechanic". Once per turn of the game, they can pick one vehicle to "repair". If that vehicle would get killed in this turn, it stays alive instead. The rest of the vehicles play the role of the "Teammates".
ExecutionThe game usually happens with all participants gathered in one place physically. When everyone's roles have been assigned, the game begins. It starts with the "Enemy Turn".
The Enemy TurnDuring this turn, all players must close their optics. The Matchmaker then tells the Hellcats to open theirs. They can use handsigns or nonverbal radio messages to decide on one Teammate that they want to kill. Then, the Matchmaker tells them to close their optics again. Next, it's the Mechanic's turn to open their optics. They can pick one player (even themselves) to repair. This player will "survive" the Enemy Turn, even if they were picked by the Hellcats. Then, the Scout opens their optics. They can point at one player and the Matchmaker will inform them silently if that player is a Hellcat or not. Finally, the Enemy Turn is over and the Matchmaker announces the "Allied Turn".
The Allied TurnNow, all players can open their optics. The Matchmaker tells them who was killed during the Enemy Turn. This player is out of the game immediately and can't reveal their identity or participate any further. If the Mechanic happened to pick the player to repair that would have been killed, the Matchmaker instead just announces that this player was saved by repairs. The main part of the Allied Turn then begins, where all players have to talk to each other and discuss who they want to kill. The players can choose one participant during the Allied Turn who will be killed. The goal is to kill the Hellcats. But since no one is obligated to say the truth during this turn, the Hellcats may try to spread misinformation. The Scout and the Mechanic may reveal themselves during this phase, if they were chosen and want to avoid getting killed by the Teammates. As soon as the decision is made, the Matchmaker tells the player who was chosen that they are killed. They are now out of the game, but other than with Hellcat kills, they reveal their role. The Enemy Turn starts again, everyone closes their optics again.
Winning and LosingThe game continues on this way until the Teammates manage to kill all the Hellcats (which means the Teammates win), or until the Hellcats have killed enough players that there is an even number of Hellcats and other players left (for example, two Teammates and two Hellcats, in which case the Teammates lose).
Since Hellcat is a very social game, the players are encouraged to really get into their roles. They can make up an identity during the game and stay "in-character", which some do very dutifully. This can be used for making the game more interesting, especially when done as a self-imposed "extra difficulty". For example, a player may introduce themselves as "I'm Cinder, an SU-8 who shoots when I see a leaf of grass bend" and then proceed to accuse Teammates of being Hellcats arbitrarily. Other Fun Additions
Sometimes, players invent new roles or change the rules a bit to suit them better. There may be more than one Scout assigned, or additionally/instead a "Passive Scout" who is not allowed to speak the entire game. Variations
In some regions, other tank types are used instead of Hellcats. Sometimes, the game is called "Wolverine" instead and features Wolverines, for example. An edgier/darker version features Teamkillers, but the fear and stigma around the associated crime is so strong that this variation is generally frowned upon.