It's Pikachu running through Super Mario Bros 1 levels. I won't comment on whether making a fangame like this is a good idea, but I will note that it felt kind of like an old romhack or bootleg cartridge.
I played on PC, and honestly the controls didn't work very well with a mouse. I found it really awkward to time jumps, and often moved instead of jumping or vice versa. I did get used to it enough to finish the first level but it never really felt solid.
I do, however, see how the controls could work well with a touchscreen. I just wasn't able to try this myself.
There were some issues with collision. Some of the obstacles I just passed through, and others I kind of hit them but was able to sort of push through the edge. It's hard to describe. I also wish there was more feedback in the form of effects when picking up a star or hitting an enemy.