Note: This list is BETA! Post here if you find a combination that isn't addressed. I haven't actually tried using this yet, I normally don't have that many interacting terrains

This is 3 terrains. Each number is a corner starting from the upper left and going clockwise. IE 1123: upper left = terrain 1, upper right = terrain 1, lower right = terrain 2, lower left = terrain 3.
1 1 1 1
1 1 1 2
1 1 1 3
1 1 2 2
1 1 2 3
1 1 3 2
1 1 3 3
1 2 1 2
1 2 1 3
1 2 2 2
1 2 2 3
1 2 3 2
1 2 3 3
1 3 1 3
1 3 2 2
1 3 2 3
1 3 3 2
1 3 3 3
2 2 2 2
2 2 2 3
2 2 3 3
2 3 2 3
2 3 3 3
3 3 3 3
Total 24 different tiles.
---------------------------------------------
This is 3+3 terrains. In other words, 4 terrain types, but 2 of them don't interact. Useful for cases where you want 4 terrains but it wouldn't make sense for 2 of them to be adjacent to each other without a transition.
1 1 1 1
1 1 1 2
1 1 1 3
1 1 2 2
1 1 2 3
1 1 3 2
1 1 3 3
1 2 1 2
1 2 1 3
1 2 2 2
1 2 2 3
1 2 3 2
1 2 3 3
1 3 1 3
1 3 2 2
1 3 2 3
1 3 3 2
1 3 3 3
2 2 2 2
2 2 2 3
2 2 3 3
2 3 2 3
2 3 3 3
3 3 3 3
4 4 4 4
4 4 4 2
4 4 4 3
4 4 2 2
4 4 2 3
4 4 3 2
4 4 3 3
4 2 4 2
4 2 4 3
4 2 2 2
4 2 2 3
4 2 3 2
4 2 3 3
4 3 4 3
4 3 2 2
4 3 2 3
4 3 3 2
4 3 3 3
Total: 42 different tiles.
---------------------------------------------
This is 4 terrains.
1 1 1 1
1 1 1 2
1 1 1 3
1 1 1 4
1 1 2 1
1 1 2 2
1 1 2 3
1 1 2 4
1 1 3 2
1 1 3 3
1 1 3 4
1 1 4 2
1 1 4 3
1 1 4 4
1 2 1 1
1 2 1 2
1 2 1 3
1 2 1 4
1 2 2 1
1 2 2 2
1 2 2 3
1 2 2 4
1 2 3 2
1 2 3 3
1 2 3 4
1 2 4 2
1 2 4 3
1 2 4 4
1 3 1 3
1 3 1 4
1 3 2 2
1 3 2 3
1 3 2 4
1 3 3 2
1 3 3 3
1 3 3 4
1 3 4 2
1 3 4 3
1 3 4 4
1 4 1 4
1 4 2 2
1 4 2 3
1 4 2 4
1 4 3 2
1 4 3 3
1 4 3 4
1 4 4 2
1 4 4 3
1 4 4 4
4 4 4 4
4 4 4 2
4 4 4 3
4 4 2 2
4 4 2 3
4 4 3 2
4 4 3 3
4 2 4 2
4 2 4 3
4 2 2 2
4 2 2 3
4 2 3 2
4 2 3 3
4 3 4 3
4 3 2 2
4 3 2 3
4 3 3 2
4 3 3 3
2 2 2 2
2 2 2 3
2 2 3 3
2 3 2 3
2 3 3 3
3 3 3 3
Total 73 different tiles.