How about creating a dungeon? For example, for the evolution of the Dukemon Cream Zone Mode, items such as Granny are required. By dropping through the dungeon.
As another example, you can obtain Omega Sword by hunting Diablomon with Emperor Dramon. Etc. Dungeons where items appear only when certain conditions are satisfied.
and please Consider also having multiple entities fighting together
I am sorry that I am not good at English.
thanks to you.