Lake Clip

Lake Clip is a speedrun strategy in the Lake Kingdom that involves clipping out of bounds to activate the checkpoint flag on the painting ledge, thus allowing Mario to warp up to it and collect a Power Moon. Because the clip is precise, it is usually only recommended for experienced speedrunners.

Execution

After collecting the End of the Hidden Passage moon, there is an extremely small gap in the collision between the two walls forming the convex corner inside the passageway. The player can clip out of bounds between these two walls by performing a precise setup:

Place Mario anywhere near the corner and move the camera as far to the right as it can go, and up far enough to get a good view of the area.
Face Mario toward the wall and position his shadow directly on top of the line that comprises the corner on the outside of the passage. This line should divide Mario's shadow in half exactly. In order to help with this precise positioning, the player can optionally crouch walk forward into the wall until Mario is in the desired position.
Jump directly forward into the rear wall until Mario begins sliding on it, and let go of the joystick.
While Mario is sliding down the wall, throw Cappy without inputting any direction on the stick. Mario should throw Cappy towards the screen, and if all the previous steps were performed correctly, Cappy should clip through the corner.
While holding Cappy in the extended position, wait until Mario lands on the ground and then roll forward into Cappy without inputting any direction. Mario should clip through the wall and bounce on Cappy. Although this will only happen if Cappy clipped in the previous step, Cappy clipping does not guarantee that Mario will clip. (There is a visual cue for this: if Cappy clips but is too far to the left, Mario will bonk instead of clipping.)
After bouncing on Cappy, move slightly to either the left or the right, and ground pound. If done correctly, Mario will land on the floor while remaining partway out of bounds.
Perform a ground pound jump while moving Mario to the left.
At the top of the ground pound jump, cap throw to the left, dive and bounce.
Wall jump against the back wall, then perform an upthrow followed by a homing shake to activate the checkpoint. At the same time, dive down into the water below as Mario toward the chest moon below.

After the clip is successfully performed, the player can collect the moon from the chest in the underwater passageway below, then warp up to the painting ledge to collect the moon on top.