Tropical Freeze Textures: the TXTR format. RTB and Parax pretty much figured it out.

[Parax]

Out of curiosity how much is known about the actual image formats used by Wii U games? I'm a lot more interested in seeing them extracted without using TexConv2, because the process of taking the file, converting it to GTX, dumping it to a temp file, running TexConv2 on it, and loading the output to actually use it something sounds painful compared to just loading the TXTR and decoding it directly (plus I'd rather not be writing programs that are dependent on leaked SDK tools). Although I'm all for it as a temporary thing if it helps figure out the header