I'm basically creating one tiny new level with one new mechanic at a time, and I'll build out the new mechanic as I come up with the idea for the next level. The first level had "nothin", just jumping and hitting the balloon. The next level had clearing gaps. The level after that had a moving platform. And so on.

After I get the enemy running up walls, I have a few other upcoming ideas. I'm going to add in disappearing platforms that fade when you step on them. I'm also going to add in alternating platforms, where one platform is "on" and the other is "off", and then it switches. I'll add in floors that move quickly in one direction. I'll add in falling ceiling blocks. I'll add in bats that swoop in from above. And I'll add in something like the lava bubbles that shoot up in between gaps that need to be cleared. I also like the lava spinners from Mario, so I'll add something like that in as well.

In the preceding paragraph, I've just described the next 7 levels, and that's just the prototype. After all the game pieces are done, I'll start to assemble the final levels for the game. Everything is coming along smoothly.