First one is easy. As soon as the logo for the dev appears just press X and you can walk forward in the cave while the logo is still there. Second one is clipping. Take something you can throw and get next to a wall and face it. Throw the thing, take damage and once the thing clipped inside you jump on it and walk in the wall. It is that easy. Though the second one is not as useful tbh

Okay so turns out you can get OoB by just wiggling next to a Wall