this is the description given by the maker of the video
(This is not the real name for this series of videos, but it is my personal name for it.
The literal translated name for 自作の改造マリオ（スーパーマリオワールド）を友人にプレイさせる is "Making my friend play through my own Mario(Super Mario World) hack", hence Kaizo(hack) Mario to the USA.
The original videos were in god awful codecs that were a bitch to convert, so unfortunately the Tool Assisted Speedruns came first to most youtube watchers.
This is rather unfortunate, as I feel you lose a lot of the "appeal" by watching those.
Anyway, watch an evil genius of a level designer subject his friend with godly skills to the must fucked up combination of creative, insane, downright ASSHOLEISH Super Mario World levels ever dreamed of.)
this game is pure EVIL
ya'll can DL it if you want to try.