In old worlds it is highly recommended to use the "optterrain" command in the console when standing on heavily modified terrain. This will cleanup excessive terrain modification data from your world database and makes the game run much smoother.

To get the console, you need to add "-console" to the Valheim command line in Steam. Then press F5 in-game and you have the console.

The "imacheater" command has been changed to "devcommands".