You can disregard the following text by watching this video: YouTube - Where does the cheese go!?!
...and because all of the following things are explained even better in the wiki.
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Basically, you're put into a random room (or you can choose your own) and there are two types of characters: shaman (or 2 shamans) and mice.
Shamans are mice with some funky painting on them and they have the ability to build. Mice are basically the players that can't build anything and their goal is to get to the cheese with the help of the shaman.
As a mouse, you have to get cheese and return back to the hole. The hole is usually the place you spawn in.
You can become a shaman by gaining points. Points are obtained by getting cheese as a normal mouse and the place you get on that round's leaderboard. If you get first place in that map you'll get 16 maps, if you get 2nd place you'll get 14 points, and 12 as 3rd place. Places lower than 3rd will only get 10 points. If you don't get cheese then no points for you. If you die, then you lose 1 point.
There are even ways to customize your mouse! You use cheese you obtain as currency and by clicking Menu and then Shop you can use it to buy things like hats, mouth acessories, glasses and even a bowtie.
There are over 60 maps and sometimes there is low gravity, sometimes mice can push each other off (most of the time you just go through them) and sometimes you have to get the cheese solely with the help of the shaman.
Beware though, some shaman tools can be used to pretty much disrupt everyone's fun, or just ensue lulz. You can use a cannon ball to throw mice off the map and it's pretty funny until it happens to you.
As a shaman, you have two choices: good or bad. And I don't mean bad as in you suck at being a shaman, I mean bad as in you will throw your mice off just for the lulz. But of course it's better to be a good shaman because it will get you titles and cheese. There is a lot to learn, like knowing how to anchor planks so you can form a bridge and cool stuff like that, but that's in the wiki (link later on in this post).
Also, as you progress with your mouse in several ways you can earn titles like "Chubby Mouse" or "Accomplished Shaman".
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There are several techniques you guys should learn in this game, like walljumping and runjumping. You can find this on YouTube or if you're familiar with games like GunZ this should be easy for you because you basically use glitches in the game to your advantage.
Careful though, there are NO censorships. So basically, you can say whatever you want. Even usernames don't have censors.
I recommend you guys use your MMOHut forum usernames as your in game name so we can all know who you are.
If you're still not convinced, here's a picture.
Post here when you're playing so people can meet up with you.
Commands:
/ban (user) - self explanatory
/w (user) - send a whisper (private message) to someone
/room (room name) - move to a room. if you're in-game, use /room mmohut
/ranking - leaderboards
/profile (user) - see someone's profile
They even have a wiki. I recommend you guys read it otherwise you won't understand what's going on: Transformice Wiki