I was thinking of ways to increase the games longevity, so what about animals having a small chance to be much larger, not only that, these monsterous animals will have special names and not despawn. These named animals will not have duplicates until the previous one dies. Having a few elusive beasts that never leave and put fear into your heart can add alot to the game, while costing little.
Where is that big BIG game hunting at?!
This also fits into the slavic, germanic lore thing you got going on here. I want to see Indrik king of beasts and live to tell the tale!
ps: next world i better see a "onep rests here" statue