What are animated brushes?

[Ofnuts]

Here is  sample brush pipe file. Load in Gimp, export as a GIH:

• Spacing: 100
  
• Cells: 3
  
• Dimension 1
  
• Ranks: 3, incremental
  

  BrushPipe.xcf (Size: 2.35 KB / Downloads: 254)

PS: rereading your post, it is possible that in addition to being gayscale, the layers should have no alpha channel. There should be no transparency if you want a "cameleon" brush, tranparency is determined by the white.