Moddable game?

I'm wondering how can you make a moddable game?
For example how could you make your own version of tAPI (for your own game of course)?

It depends how moddable you want it.. you could create mod tools for your game that include a map editor (which could even load custom user graphics) mod tools for custom characters/scenarios/missions etc. You could even allow users to create new enemy movements etc with a custom scripting system.. there's no easy way to do all that though, it's extra work if you want to supply the tools but protect your original source.

Alternatively you could just open source your game and it will be 100% moddable, the (relatively minor) catch being users would need F2.5 to make use of the source project files.

A lot of Fusion games have included level editors. Regarding scripting you could have all your scripting in Lua and load in the scripts on startup. This would relieve the need for Fusion. Regarding graphics/sound fx you could also store them in a subfolder and load them in on start.

It's possible but you'd want to be mindful from day 1 to do everything you want moddable externally. If you tried to patch it in at the end of the development cycle you'd be ripping out 90% of your code. I would also suggest that it would greatly extend your development time as Fusion is optimised for internal resources. You'll be crossing a lot of bridges nobody's really crossed before and probably encounter some rare situations that haven't been overcome by other users, so the help may not be there when you need it.

cave story had a fair bit of modding. it used a lot of lua from memory
thing is tho - it began its life as mmf, but i think was re-written in C++ which had the modding.

Thanks guys! Lua for scripting sounds as a good idea and I will try how that will work out. (I've learned a bit of Lua before c: )