The Informant is a very powerful manipulator that is able to kill a player and steal their identity. This can be especially useful if a certain player is known to be a reputable Town role, such as the Mayor, an Investigator, or a Sheriff.
If there is an Incense Master in play, it is frequently a good idea to have the Triad not kill for one night so an Informant can claim his target and either have the Incense Master clean the target or use his personal cleaning if it is enabled.
If there is no Incense Master and the Informant has personal cleaning enabled, have the Triad kill normally as the Informant claims a target. Smart towns will notice that someone was cleaned and that the Informant has made his move.
If there is no Incense Master and the Informant does not have personal cleaning enabled, it may be wise to have the Triad not kill the same night the Informant takes action, so the Town doesn't know whether the Informant has made a move yet.
If the Triad knows a target will be healed, then both the Informant and Enforcer/Dragon Head can attack the target, which will negate the Doctor heal and allow the Informant to assume his victim's identity.
It is generally not advisable to use the Informant's ability early on in the game as the Informant will unable to do anything more for the rest of the game besides be an extra vote. However, if there is a revealed Sheriff or Investigator, disguising as someone else can still sow confusion amongst the town, as they will think the Informant's logical target (as they may see two Triad deaths in a single night) would be that role, when really it is not. The Town might no longer trust that role, or even lynch him, netting you two kills while remaining safe.
If you are discovered by an investigative role, do your best to lie your way out of the situation to survive to the next night so that you may disguise. Good lies can involve claiming to be a Jailor or Bus Driver, whereupon you claim that you will prove yourself tonight as those roles by either jailing someone or bus driving two people, as the Town will believe you as you cannot fake these things. If the lie is successful, you can now evade lynching. Even if you are unfortunately discovered the next day, you have granted your fellow Triad members one more night to kill, which can sometimes decide the outcome of a game.
It is usually an extremely poor decision to disguise as a revealed Mayor. If cleaning is off then you will be instantly found, as your corpse will appear to be the Mayor and everyone will know the "Mayor" is actually a Informant. If cleaning is on, you have a bit better of a chance, but often you will be asked to display your voting power after a cleaned body comes up, which will almost positively lead to the death of you. Don't do it.
The best role you can disguise as is a revealed Marshall if cleaning is on. Not only will you take a confirmed Town role, but there is no way to reliably prove you're Informant as asking a Marshall to initiate a multi-lynch for the sole purpose of confirming if he's a Informant or not is unheard of. Most Town will naturally assume you're not scum for the remainder of the game, leading to an easy victory.
When disguising, the Informant will appear to die the following morning,
If the option "Cleans the target's role" is enabled.
The message "We could not determine the player's role" will appear.
The Informant will be told their target's Last Will.
If the option "Cleans the target's role" is NOT enabled.
The target's role will appear as belonging to the Informant's previous name.
The Informant's own Last Will be left with his older name's dead body. Making for some interesting ways of getting Town to lynch people, for example disguising as a Sheriff and leaving a fake Last Will saying someone is evil.
Informants retain their role and have no abilities after disguising as someone.
When disguising as the Mayor, the Informant will not retain the extra votes.
Informants will not participate in Mason or Cultist night chat but will be in their allies list, therefor disguising as a very talkative Cultist or Mason is generally a bad idea.
If a Informant wants a Incense Master to clean his target, the Incense Master should select the same target at night and not the Informant's name.