The model UVs of Magma Cube have been changed in recent beta 1.21.50.28, and the updated texture uses the same filename as before. As a result, some marketplace resource packs (e.g. Classic Texture Pack) have not been updated, and their Magma Cube textures are broken (see image).

This can be fixed by simply renaming the new texture file from magmacube.tga to something like magma_cube.tga or magmacube_v2.tga, just like what has been done to the new bat texture introduced in 1.20.50.22.

Full list of affected resource packs:

• Classic Texture Pack
• Plastic Texture Pack
• City Texture Pack
• Cartoon Texture Pack
• Pattern Texture Pack
• Candy Texture Pack
• Steampunk Texture Pack
• Natural Texture Pack
• Master Chief Mash-Up
• Greek Mythology Mash-Up
• Chinese Mythology Mash-Up
• N7 Mash-Up
• Halloween Mash-Up
• Dragonborn Mash-Up
• Vault-Tec Mash-Up
• Adventure Time Mash-Up
• Festive Mash-Up 2016