Maybe you will need a new world. I played mistlands on my pre H&H world but I did reset the mistlands biome with the world upgrade mod. The terrain is not much different from mistlands in a new world, it felt like there were a lot more dverger structures (but not more infested mines).
The problem is, mistlands also changed world generation. I tried upgrading to mistlands world gen with the mod but that ruined the terrain inside of my base so it wasn't an option for me.
I just started a new world and transfered all of my stuff (I recommend changing inventory size and weight limit temporarily for this with valheim+ mod).

I have never messed with the mods that can change worlds, and I've kept playing on the same world since (almost) the beginning of early access. It works fine for me, but maybe not for everyone.

There is a mod called Upgrade World, it can add new content and such to old worlds. I used it to add tarpits, mountain caves, and to upgrade the world to the Mistlands patch biome distribution. I can't remember exactly, but when using to change your world to the new patch distribution levels it basically resets everything beyond 5000m from the worlds center. Anyways, seems to have worked well on my world which was made couple a couple days after the game originally launched. Just make sure to read the instructions and make back ups if you decide to go that route.

Also, what would you recommend? We have no problem creating a new one, if it is to live the experience better, what if, we could only take the items that enter the inventory of our characters, right? At least the characters would be preserved, I understand

Originally posted by Peron:

Also, what would you recommend? We have no problem creating a new one, if it is to live the experience better, what if, we could only take the items that enter the inventory of our characters, right? At least the characters would be preserved, I understand

Yes, you can move items to a new world in your character's inventory. You can also make multiple trips to get everything you need. Make chests in the starter area to drop stuff there.

mm I imagine haha, it's going to be a bit rough, I think the best thing would be for one of my friends to create the world, so I can enter between mine and his to speed up the process

Yes and no.

Mistlands will generate in areas where no one has explored within around 500m. That means if any of your friends went there it won't work right. If you have large unexplored areas on your map then it will probably work. If you go this route, your chances are better if you sail east or west, because ashlands and the north eat up the north and south.

On the other hand, map generation has changed with the new update and the Mistlands you get on an old map won't be as large and it may be harder to find one that isn't a bunch of rocks sticking up out of the water.

A new map is probably better but you might be able to make it work on an old one.