The enemy mobs in the Nether—especially in the Halloween Mash-up Pack—have incorrect textures.

The enemies display incorrect textures—for example, Piglins and Zombified Piglins, including their baby versions.

To reproduce the issue, you simply need to encounter any of these; I will show the expected result in images, as they speak louder than words.

The result is disappointing; they simply used the same vanilla Minecraft model for the Piglins and Zombified Piglins.