Originally posted by I Gods Grace I:

An important thing to note is that the Mistlands biome will only generate in areas you have not yet discovered. Therefore, if you have explored a lot of your world, you might be better off starting a new one in order to actually be able to travel to the Mistlands.

I didn't plan on exploring much. Just enough to get to stone and start making a base out of it for fun until mistlands goes live on stable.