Banned by mistake
Before assuming your ban was by mistake, read over the reason you were banned carefully. If after reading the reason carefully and considering your past actions you are confident the ban was a mistake, contact the Scratch Team using the appropriate method and explain why you think it was a mistake.
Do not create alternate accounts (or use any alternate accounts you already have) to get around bans. This will make you seem less trustworthy to the Scratch Team and they will likely extend the time of the original ban.
Involving others or publicly discussing bans
Discussing other users being banned is not allowed and any such content will be deleted. Do not encourage other users to make projects, forum posts, etc. asking you to be unbanned, as that will not help your case and may make the Scratch Team less likely to unban you for causing drama. Also do not post any questions related to the ban using an alternate account, as that would be considered ban evasion and potentially causing drama.