Janitor

Mechanics

 * If there are no kill capable Mafia roles left you will become Mafioso.
 * You can talk with the other Mafia at night.
 * Your cleaning attempt will be successful if your target dies for any reason, including leaving.
 * The cause of death will still be revealed to the town, which will prove their role if they were a Vigilante committing suicide or a Bodyguard dying while protecting their target.
 * After you have successfully cleaned a victim, you will receive a message about their role.
 * You will be able to read your victim's original will by clicking on their name in the Graveyard. Everybody else will see a blank will.
 * The Retributionist cannot revive victims you have cleaned.
 * An Amnesiac can attempt to remember the role of a victim you have cleaned. However, nothing will happen if that role was unique.

Selecting Someone to Clean

 * It is very important to clean Town Investigative roles because they are almost guaranteed to write something in their Last Will that is important to aid the townies in lynching. Always clean them, especially if Mafioso or Godfather decides to kill a known Town Investigative. You can later disguise to be one of the Town Investigative roles as well. Additionally, Consigliere can benefit from the information obtained, and it will often help them prioritize their investigations.
 * Retributionist are also unable to revive your cleaned targets. This can come in handy when dealing with a revealed Mayor, Jailor, or other important roles who often left important last will.
 * Even when you are cleaning town roles that seem has no importance for the Mafia in their last will (such as Doctor, Witch, or Survivor), it still can be helpful to confuse the townies in a situation where the role list is random (for example, the Ranked Mode or All Any). This situation is more likely to be useful when you're likely to be lynched next day or the game would be likely to end because there is only few players left, and you would like to use all of your three cleanings. However, keep in mind not to waste your cleanings because Janitor can be extremely helpful, as mentioned earlier.
 * If you're in doubt about when to use your cleanings, you might consider cleaning a person who is leaving the game or getting disconnected ("apparently committed suicide"). Those who left the game are incapable of telling a medium their true role, are usually not investigated and not watched (usually 1st night), and they are guaranteed not to retaliate! (ex. Veteran, Werewolf). This always sheds doubt especially on semi-random role lists, as townies will be unsure of the existence of that role.
 * A Disguiser is your best friend. Due to your ability to dissolve any connection between the target and their role, this allows a skilled Disguiser to assume that person with essentially no retaliation. However, a living Medium can still find out the person's role. This could also lead to the Disguiser being shot by a Vigilante or lynched the next day.
 * Since the Survivor is a very low threat and isn't bothered with much, killing, cleaning and having a Disguiser can be an alternative strategy, though it is very rare.

Taking advantage of your Cleanings

 * You know your target's role, so saying you are a Medium the next night and revealing their role, claiming they told it to you can support you. With this way, you can trick the town by saying in the name of the dead people, for example "The (name/role) says X is suspicious/Mafia/Neutral Killing" while X is not a part of the Mafia. Moreover, you can do other things to make you naturally believed as a Medium by becoming a messenger (i.e. if Jailor has executed a townie, you can say "the jailed townie is getting mad at the jailor").
 * However, keep in mind that sometimes it's normal to have two or more Mediums, and then the real Medium may call you out because the dead people will alert the real Medium during the night.
 * This strategy may have a backlash when you're standing out as Medium for too long without Mafia trying to kill you, especially when you have revealed a lot of "important" information publicly. The townies might think you are the Janitor instead. Many Towns will rapidly lynch any Medium claims when it becomes clear there's an active Janitor.
 * An alternative strategy is to pretend to be a Medium and say that someone dead was disguised, giving the townies reason to lynch a target of yours. If you don't clean they have no reason to suspect a Janitor even being on the mafia's side. Remember that this will expose you when your target gets lynched and their role is revealed; you can sometimes survive after making a false accusation by claiming Executioner, but it's best to do this when a successful lynch will give the Mafia the majority regardless.
 * Another option you can do is to pretend or role-play to be the role that you cleaned, especially because only you can read (and copy) your target's last will. Many unique roles are rarely claimed due to the ease with which they can be counterclaimed; cleaning can open these up to the entire Mafia (although informing the Mafia of this risks alerting the Spy.) In all cases, be aware that this risks getting you exposed by a Medium and that these claims trust the Town to not dig any further and demand conformation going forwards; usually the Town won't ask for more confirmation once you're "confirmed", but it may happen if the game drags on or if something else calls attention to you.  Regardless, when a cleaning allows them, some of the most powerful claims are ones that the Mafia is rarely able to make (and which therefore are less likely to face reflexive scrutiny):
 * While it's dangerous, claiming Jailor is sometimes plausible after cleaning the Jailor, since the Town will frequently not bother to ask for additional confirmation, trusting the real Jailor to sort you out if you lied (and unaware that they're dead); you can also use previous records of who the Jailor jailed from the will in order to get them to confirm you.
 * Similarly, the Veteran is normally a dangerous role to claim because it's unique; but after you've cleaned one, it becomes incredibly easy and will discourage Investigators from examining you in the future.
 * Transporter, usually an impossible role to claim due to the need to produce a will that the people who have been transported can confirm, sometimes becomes available if you steal the detailed will of a transporter; however, you need to claim quickly, because the Town may notice if the will ends early. Alternatively, you can tack on entries at the end that transport you with Mafia members or with people who died; one or two Town confirming the will's transportations will often be sufficient to let you pass as a Transporter.
 * In Ranked and other modes where roles are defined by general category, successfully cleaning a role opens up that entire category as a safe claim.
 * After cleaning a Jailor, you can use other strategies that rely on the Town's assumption that the Jailor is still alive, too. For instance, your Godfather can claim to have been jailed as a way of explaining his night immunity, if called out by a Serial Killer or Vigilante
 * Giving the other Mafia members information based on your cleaning is valuable; but you have to weigh this against the risk of the information getting leaked to the Spy. If you do want to tell the Mafia the role of someone you just cleaned, it might help to just say that role and nothing else, so a Spy won't know if you're a Janitor reporting who you cleaned or a Consigliere reporting who you investigated.

After Out of Cleanings
When out of cleanings, don't give up! You still contribute to the Mafia with voting, sharing out strategy in the Mafia Chat, or perhaps becoming a Mafioso later.
 * If you've already pretended to be as Medium (and you're safe that there are no actual Medium left), you can continue the disguise strategy or simply saying nothing "because no townies are talking".
 * If you have no cleanings left sometimes it can be a good idea to try and take a hit for a more important member of the mafia (Godfather, Janitor with cleanings left, etc.) Try pulling attention to yourself to draw it away from others. Only do this if it is clear that another Mafia is in danger of getting lynched/killed or if they have a more important role in the Mafia than you. Keep in mind you do not need to be alive to win when the Mafia kills everyone.