You can play alone or with a friend.
I just want to make some notes:
1. Don't say it's impossible. It may be challenging at some points, but I tested it all, and it's all possible.
2. Sometimes you'll need to hold E/CTRL instead of tapping it.
3. Try to play through the whole thing before reviewing, OK? The first level really doesn't reflect overall difficulty.
That is all. Have fun!