Valheim is a survival game in which the player starts from scratch entirely. You need to get materials and hunt in order to survive and in the future to create equipment, build a shelter, and so on. During the exploration of the world, you can also summon five different bosses, which are in different places in each world, thanks to the random generation.
This fact greatly complicates the search for them, especially for speedrunners seeking to set world records. But NickRawcliffe was lucky: he managed to find all five of the strongest monsters in Valheim and defeat them in just 73 minutes.
However, there is a caveat. All speedrunners have set the rules for such a record in Valheim. A set of laws states that players do not need to start with a new character in each “run”, and therefore a character can immediately be at the maximum level with many items.
This detail clearly simplifies the achievement of NickRawcliffe and in the video you can see that the user already had things with him to summon all five bosses.