Offences against Public Tranquillity are dealt with in Chapter VIII of the Penal Code.

Unlawful Assembly (S141 & 143)
If 5 of more of you gather together with the common object of committing a crime or a mischief, you are a member of an unlawful assembly, even if you specifically play a different role from the others in your group and/or even if not all of you knew the full details of what it was that the rest of you in your group intended to do and/or commit.
If convicted, you can be jailed up to 6 months, or with fine, or with both.

Unlawful Assembly with deadly weapon (S144)
Any member with a deadly weapon in an unlawful assembly can be jailed up to 2 years, or with fine, or with both. Even if only one or more persons in the group possess(es) a weapon, the law treats the rest of you as being equally culpable.

Rioting (S146 & S147)
If you are part of an unlawful assembly and force or violence is used, every member is guilty of the offence of rioting even if the degree of participation of each of you is different. You can be jailed up to 5 years and can also be ordered to be caned.

Rioting with deadly weapon (S148)
If you are part of a riot and any one or more of you is armed with a deadly weapon, each of you is equally culpable for the use of the weapon(s), and you can jailed up to 7 years and shall also be liable to caning.