The challenge here is, What is the minimal set of terrain tile types to be able to build arbitrary terrain in a side scroller?  In theory, you don’t need minimal sets of anything if your blocks fit exactly into a square.  You see that all over; especially in the older Nintendo classics.  I want to be able to use a more diverse set of borders though… and I *think* the above image represents a complete set.

That’s not to say that each type of tile won’t have many distinct tilesets… Hopefully I will have quite a few distinct tilesets for this game.