THIS CONTAINS SPOILERS!!!
The website isn't complete yet.
This is a link to the game! Here's the link: Undertale. It isn't Free.
Here's info and tips.
Here's an image:
Here's three things you need to know:
Temmie Village
Tem village is a village in the dark room with glowing mushrooms. Go to the first mushroom and turn it on. You will see two glowing paths. Go left, light the mushrooms until you come to a dead end. Go right and go down. Eventually you will go on a short, invisible path to the Temmie Village
Omega Flowey/Asriel Dreemur
When you are playing the pacifist you will fight Asrier Dreemur or Omega Flowey. To fight Asriel become friends with Papyrus, Undyne and Alphys. Sans comes automatically with Papyrus. Do not forget to not kill even a single monster. That will ruin everything. When you fight Asgore if Toriel stops him destroying the mercy you will fight Asriel. If you forgot to befreind one of them you have to fight Asgore and after Asgore you will fight Omega Flowey.
Key to sans room
The key gives you access to sans room. To get the key, you will need to complete and reset the game. Play again and when you come to the corridor with sans in it save before talking to sans. That is very inportant. Talk to sans and he will probably say something different. Quit the game without saving and start it again. Repeat until you get the key. When you got the key go to sans and papyrus house and open sans door. It will be dark but continue walk forwards. Papyrus will come in and turn on the light and you will see the secret behind the not very big room. Bonus:Go to sans drawer and you will find another key. Now go outside and go to the left backside of the house.You can go in there and press z and probably you will find a secret door and unlock it. The extra secret room.
To learn more about UNDERTALE check out this Undertale Wiki!