Not sure what kind of ''fight'' you expect out of this, without any context.

Terraria and Valheim have a lot in common, in the sense that they are both survival, crafting and building games with exploration ellements.
Both have similar crafting stations where you have to place upgrades nearby, and have to mine minerals and build bases.
As well as fighting bosses to move the game forward.

But i do think that the playerbase is quite different. Terraria being a 2d game.