4Game

Unless you really need a bunch of artisan tables, or you're the sort that can never find their keys, there's not currently a reason to re-fight bosses, other than hanging their trophies, or if you just enjoyed the fight. I enjoy reward incentives, though, as do most. I think it would be cool to have an extra boss drop that only occurs after their trophy is hung in a world. A special drop that would provide gear infusions.

The infusions would be for all weapons, shields and armor. They would provide small buffs, and the buffs would be upgraded the same way weapons are. If you have a level 2 iron axe and want a level 2 boss infusion on it, you would kill that boss twice for the drop, just for that one weapon. If you want a level 3 infusion, you need to kill the boss a 3rd time and level the axe to 3. Even small buffs would be helpful though, so they would require a higher level forge even for the lowest level, so they're unlocked somewhere around iron or silver age. Buffs would be permanent on that gear, which would require grinding the bosses and materials for new gear if you wanted the infusion on the next tier of equipment, or wanted a different infusion on the same tier you already have.

Eikthyr would provide a reduction in stamina usage to any tool, staff, weapon or shield that it's equipped to, by a small, flat amount. On armor, it would provide a 1% movement speed buff per level, meaning you'd never fully remove the penalty of heavy armor, but if you choose this over other buffs, you'd take most of the sting out of the movement penalty.

The Elder would greatly increase the durability of any gear with the infusion.

Bonemass would obviously be poison damage on weapons and staves, and I mean that to add poison damage to summons as well. Poison resist on shields. This whole idea came from the unused asset in the game called "Bonemass heart" that looks like it was meant to be a permanent health upgrade. That's not in the game, but the infusion for armor would be a few health points per upgrade level.

Moder would be frost damage on weapons, resist on shields. On armor, enemies striking the player would receive the frost effect (but no damage) for a much shorter amount of time than being hit with frost damage, scaling based on number of pieces with the infusion and their level.

Yagluth would be fire damage on weapons, resist on shields. On armor, it would provide a very small amount of health regen.

The Queen would provide a small, flat amount of eitr leech on hit for non-staff weapons, a small amount of eitr regen on shields, headgear and capes, and a small flat amount of eitr stat on chest and leg armor. An infusion on staves would reduce eitr costs by a small amount.

I feel like the permanent choice and amount of grind required are decent balancing factors, though more could certainly be added. Thoughts?