.brtex

A Binary Revolution Texture (.brtex) file is a file similar to a BRRES, however it only contains textures. There is only a single instance of this file used in NSMBWii, and that is the icon shown when Home Button inputs aren't accepted (Home icon with the denied symbol). It can contain texture files, but that's really it.

Opening BRTEX Files
You can open BRTEX files using BrawlBox or BrawlCrate. Both tools also support viewing and replacing the texture inside it.