WOLFWORLD is an event world that was introduced on the 2nd day of Player Appreciation Week 2015.
If you wish to challenge WOLFWORLD, you would need a Wolf Whistle. There are 6 different Wolfworlds, with the names WOLFWORLD_1 to WOLFWORLD_7.
Entering the world "WOLFWORLD" via a door or the world selection screen would not teleport you to the actual WOLFWORLD. It will lead you to a tribute of WOLFWORLD.
If you attempt to enter it, it will say "That world is beyond you at this time".
You can win one of the following items when you finish Wolfworld: