This is a game that punishes you for entering a biome before you are truly ready to tackle them. You really need to max out your equipment as much as you can before entering a new biome or the game will kill you. It's that brutal.

And you *can* complete all 5 bosses solo. How to do so might not be obvious at first, but it's just a matter of studying your environment, what effects your weapons make on certain enemies, and learning how the world works.

....And persistence in the face of constant failure and frustration, because this game has plenty of that. Persistence will always get you over the line.