1. No chat, roleplay, hangout/chilling/party/etc. servers. The Master Server is for netgames where people are actually playing the game the way it is intended to be played. If you want to chat, roleplay, or hangout, either use a chatroom or host without advertising on the Master Server.
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7. Use the correct gametype for what you are doing. If you're in coop, you should be completing the levels. If you're in Match, you should be shooting each other. Do not use coop mode in maps that do not support coop mode. Do not use coop mode when you are actually fighting each other. If you are fighting each other, use match. The Master Server shows which gametype the servers are currently playing in, so make sure that the gametype is actually accurate to what you are doing, so that people will not come in expecting to do one thing when you're really doing something else.
* Hide and Seek is allowed in SRB2 as long as you use Tag mode.