Formation Menu Clipping

Repeatedly closing and opening the formation menu allows the Links to clip into and even through actors and adjacent tiles.
Examples for actors are NPC, movable objects like blocks, and Gem Barriers.
Because you need a source of momentum there are generally two types to differentiate:

(Reuniting) FMC

This method uses the movement of non-Green Links reuniting towards Green.
The Links must be positioned in a way so that the actor you want to clip into is between them.
For the actual clipping, the Y input has to be performed 1 frame later than with the Roll method (see below).

1. Position the Links as mentioned above
2. Press Y twice before the reuniting Links touch the object you want to clip with
3. Press B to close the menu and quickly re-open it (B, wait one frame, Y)
4. If the Links respawn next to Green, it means your Y-input was too late. If they don't move at all, you didn't wait for one frame => you did (B,Y) instead
5. Repeat this procedure until the Links have clipped far enough into the object

You can use a C-Formation to move the clipped Links out of the actor and into a desired spot.
However, this only works if the clipping Links are close enough to Green.

Otherwise you have to close the menu and press X on the next frame (B,X).
Simultaneous B+X inputs or a delayed X input will cause the clipping Links to spawn next to Green and you will have to start all over again.

8-3 Gem Barrier Skip

Roll FMC

This method uses the momentum of Green performing a roll.
Its concept is rather direct: Green starts a roll, then uses FMC to clip and effectively roll through an object.
A notable difference is that for the clipping part, you want to press B followed by Y on the next frame (B,Y)

1. Put Green next to the object you want to clip through
2. Start a roll, then press Y to open the menu
3. Press B to close the menu followed by Y on the next frame (B,Y)
4. If Green gets pushed out of the object or respawns, you either pressed B+Y simultaneously or your Y-input was too late.
5. Repeat the procedure.

Note that once the roll animation has finished, Green has no way of getting momentum again and will respawn unless you combined FMC with GBA OoB.

Snow Wall Skip

In connection with OoB