i thought of this as a "final" research for adventure tree: adding a huge quest divided by steps who leads to something epic!

example:

after a bit of research you unlock some new research "misterious writings" that allows you to go in 4 5 ruins all around the world and find some old tablets you cant understand

then the next research will be decipher chapter 1-5

any chapter will lead to find some ingredient for a formula searching the appropriate beast (some spider leg, a troll ear, a drake tooth etc) then you just go and hunt that beast (or that place, can be an island or a forest, dunno)

the final chapter then is gonna be the explanation on how to use that formula to evocate a powerful ancient demon, you will need to go on the edge of the volcano, with the appropriate reagents, and the mighty demon will appear and if you defeat him he ofc is carrying a powerful artifact (or maybe he surrender and just join your army, at choice)

edit: also thought you can avoid fighting sacrificing your 3 young virgin daughters, if you like