Use "z" to pregress through dialogue and press "x" to skip. Use the arrow keys to move your soul. If it's red, it's normal movement. If it's blue, there's gravity (hold the jump key to jump higher). When the screen rotates (for example, upside down), you can still press the up arrow to go up, but since the screen is upside down, from your PERSPECTIVE you're moving down, so it's like the controls are reversed. Blue attacks mean stop, and orange attacks mean move. When the colors invert, stay on the black. Also, press "h" to heal, but you can only do that 8 times.
Thanks to Toby Fox for creating Undertale Inspired by Last Breath by ZerJox