Lots of arrays, dictionaries, time in general... and I'm still nowhere near done with anything x)
I watched one too many Paper Mario mod video, making me want to make my "own" take on that... by mixing and matching ideas from a bunch of different other games.
I explain some more things in the video description directly, if you're interested.
If you're curious as to how certain things were made, feel free to ask. I can't vouch for the efficiency of the methods I've used, though ;)