The Special Boarder shown for Tetris DX when booting the SGB2 is actually the standard one used by the Super Game Boy, it should be a RED BRICK WALL with TETRIS DX name in Graffiti style on it.
When Tetris DX is played through Super Game Boy 2, a different border is displayed than when it is played through the original Super Game Boy. This said, the "2" border can be accessed in the original by putting Tetris DX into a Game Genie into the Super Game Boy, as the Super Game Boy 2 verifies whether the internal accumulator value is FE during bootup to determine whether it is Super Game Boy 2.
The Game Genie boot ROM bypasses the internal accumulator telling the game to load the Super Game Boy 2 features.
The Special Boarder shown for Tetris DX when booting the SGB2 is actually the standard one used by the Super Game Boy, it should be a RED BRICK WALL with TETRIS DX name in Graffiti style on it.
Standard Background that is shown for SGB: https://tcrf.net/images/9/97/Tetris_DX_SGB_1_Border.png
Unique Background that is shown for SGB2: https://tcrf.net/images/e/ef/Tetris_DX_SGB_2_Border.png
tested with genuine Tetris DX Cart and ROM.
Info from: https://tcrf.net/Tetris_DX
When Tetris DX is played through Super Game Boy 2, a different border is displayed than when it is played through the original Super Game Boy. This said, the "2" border can be accessed in the original by putting Tetris DX into a Game Genie into the Super Game Boy, as the Super Game Boy 2 verifies whether the internal accumulator value is FE during bootup to determine whether it is Super Game Boy 2.
The Game Genie boot ROM bypasses the internal accumulator telling the game to load the Super Game Boy 2 features.