I know basically nobody runs this game and is going to to see this, but I figured I'd share it anyway. In 4-1, there's a big pipe that you can't get past without using invisible blocks. Turns out, if you do a full jump from the edge of the bush sprite between the two goombas that spawn next to said giant pipe, you can land a wall-jump. I've gotten it a few times before, though it seems a little rng dependent on the goomba positions and probably just needs more skill then I have.