Your bot used message commands but you switched to Slash-Commands? Use this Plugin to send your bot's users a message when they try to use your old commands

Well, you could also just use this as an auto respond for specific phrases actually

1. Add https://antimessagecmds.mikbot.stckoverflw.net to your PLUGIN_REPOSITORIES environment variable
2. Add antimessagecmds to your DOWNLOAD_PLUGINS environment variable
3. Add MESSAGE_REGEX to your environment variables with the following value:
   1. PREFIX(COMMAND)(.*) (Replace PREFIX and COMMAND with your old message-command prefix and a | seperated list of commands the bot should react to, or just one command)
4. (Optional) if you don't want to use the default translated message, you can add RESPONSE_OVERRIDE to your environment variables and set a custom message