Hi Raymond, I like how you used pixel art, which matches the theme very well, to create this game's assets. When I saw the title "Train Jump," I assumed that I will control a train and jump between platforms. Your game is very close to what I wish to see! I really like the background design, but sometimes the mountains just disappear for seconds. Also, the train's movement feels very smooth but a little bit slow. If you can make the train "heavier," it will possibly be better.
Overall, the game is simple but fun. I would suggest that more mechanics can be add to make it more fun. For example, adding some traps or coins to be collected. (These are my thoughts though...) This art style reminds me of Mario so I'm expecting more mechanics. I still love how you made an "one button game" using this train theme!