Ok so for my MMO I was going to implement Item Crafting.
This is when you take two items and use them together to create a new item.
I wanted it to be like you could get raw materials from anywhere, including dropped by pokemon, and be able to get to really complicated items just by crafting raw items.
Some of these would have in-battle effects, and some of them would cure your pokemon, etc. So essentially you could make a couple of cures from items you've picked up whilst playing, similar to Skyrim or something.
NOTICE: I know some of these aren't as simple as 1 + 1 = 2, e.g. soybeans + wheat = soy sauce so try to interpret some of these loosely. If I was really accurate it would be so complicated.
It's really fun spriting items and trying out different textures!