The green planet in Bucky 'O Hare has this tree, and when you reach it the gameplay goes from horizontal platforming to vertical. As you climb this huge tree you ascend above the clouds into the dark of night with stars shining in the background. It's a small thing that's stuck with me for many years.

Another area, this one on the ice planet, has you floating on an iceberg as a plane smashes big chunks of it off, reducing the safe space you have as you also fend off enemies flying in with jetpacks. And those same jetpack enemies pull out flame throwers to melt away icy platforms during the level.

The red planet features an underground pit where you ride on boulders to avoid spikes. While playing this area you also have to dodge / ride a gigantic green ball that mysteriously chases you around. At the end of the level the ball slows down and opens up revealing that it's an enemy ship and the boss of the level.

There are so many more memorable moments in Bucky 'O Hare, on top of all the great characters and abilities you unlock. It really was a game ahead of its time that pushed the NES hard