From Hard Drop Tetris Wiki
The Horse Opener is an opener that resembles the shape of a horse. This meme opener is impractical and is only used to show off 🐴 - one can squeeze out a T-Spin around the T piece. It was created by Commando.
Horse Opener can be performed with an S/Z I bag.
The setup can be mirrored. This can be used in games like Tetris Effect: Connected and Puyo Puyo Tetris to have the horse "stare down" the left player's field, if performed on the right side of the screen.