It seems to me that Valheim has some difficulties with servers, it mainly concerns optimization. This is especially noticeable on very researched maps by the host and at the same time with a large number of delivered objects. But we're talking about ideas:
1. Server intrusions. The players on the one hand, when creating the server, allowed the intrusion. and the players on the other side, having prepared themselves well, will get on a Drakkar, go out to sea and use the horn to summon a portal to another world. On the other side, players will hear a horn (you can make a reference to Ragnarok) which will determine the location of the invasion. The skin of the invading player will be replaced with the skin of the cursed Viking Drakkar on Naglfar and several more drakkars will invade for interest, depending on the bosses killed. They will have mobs in similar skins called "Cursed". everything will be covered with fog and there will be hella in the sky. Intruders will be reborn on Naglfar before its destruction and will be able to steal all the loot there. if the sewn-up manage to fight back, then as a reward, a chest with a bunch of equipment will float in place of the destroyed Naglfar, which cannot be reached without such a pvp event. I would suggest adding parts of Valkyrie armor there that can be used to improve one of the 4 sets: warrior, archer, mage and rogue (thief)
2. Odin's Arena Build a portal and use the horn to unlock it. Behind him is a large arena at death on which your loot is not lost, but for that the gate will close and you will have to craft another horn to unlock it. the arena will be according to the difficulties and rewards that will fall out in front of the gate in the form of a temporary chest. Again, the top of the reward will be parts of the Valkyrie armor. which you can reforge and make one of 4 sets.