Imagine if you will a room full of your kills. You stare at them and swell with pride and vigor as you recall each battle. The boar that tested your fortitude. The fuling brought low by your skill. You are ready, these memories at the front of your thoughts, honing you for the battle ahead…
We know how the comfort system works. This works similarly, except different trophies provide small buffs to different stats. Each trophy only provides a 1-point boost to one stat, but they stack with others for a nice little buff for the day.
Damage
Armor
Health/Stamina Regen
Speed
If you have all trophies, you might only reach 3-5 points in each, but that would make it worth creating a room dedicated to trophies. This isn't a design to make a person powerful. It is a design to incentivize trophy hunting and display.
Source: https://www.reddit.com/r/valheim/comments/mem4ut/trophies_offer_passive_bonuses_like_comfort_bonus/