How about the Yoshi module? The one I built has 1500 lines of C++ code (in addition to some intensive modification of the Mario module). It took me 4 months to sort out all of the bugs. Among the issues I had to deal with was how to keep the Yoshi animation from being broken when he sticks his tongue out. Also, I had a lot of trouble keeping Mario from getting stuck in the ceiling. The height of his and Yoshi's combined sprite is greater than 32 pixels. Thus, I had to cut off the top portion of his collision footprint.
The next hardest thing was Caped Mario's cape projectile. I still have a few bugs. Do you know that sometimes, Mario will not go into a walking sprite again after twirling his cape?
Slopes were not too difficult for me. I only have 22.5 and 45 degree slopes. The only slight flaw is that my Mario cannot slide down a slope when a player pressed down unless Mario walks up and down the slope for a few pixels at first.
The next hardest thing was Caped Mario's cape projectile. I still have a few bugs. Do you know that sometimes, Mario will not go into a walking sprite again after twirling his cape?
Slopes were not too difficult for me. I only have 22.5 and 45 degree slopes. The only slight flaw is that my Mario cannot slide down a slope when a player pressed down unless Mario walks up and down the slope for a few pixels at first.