So what are you trying to do with the scales? You've declared the scale tissue, but you haven't declared the material, and you haven't yet done anything with it. If you want scales at the same time as skin, you'd probably be able to do something like [TISSUE_LAYER:BY_CATEGORY:ALL:SCALE:TOP:BY_CATEGORY:SKIN]. Maybe. Thinking about it, this might be a little more complex than I initially thought.
If you're wanting them to be actually made of dust, then that's not all that hard. Let's say you wanted the main "bulk" (if one can call it that) of the creature to be dust/gas with flames trailing off. The "flame" material already does quite a good job of simulating gas, so we can use that as a base.
[USE_MATERIAL_TEMPLATE:DUST:FLAME_TEMPLATE] #Designated as "DUST" because we'll use FLAME_TEMPLATE again later
[STATE_COLOR:GAS:GRAY] #Wouldn't make much sense with red dust
[STATE_NAME:GAS:dust] #These are being changed so the "dust" isn't referred to as flame
[STATE_ADJ:GAS:dust]
[MAT_FIXED_TEMP:NONE] #So it doesn't burn things
[DISPLAY_COLOR:7:0:0] #Light grey
Everything else can stay put. Now we need to declare a tissue to apply this to:
[USE_TISSUE_TEMPLATE:DUST:FLAME_TEMPLATE]
[TISSUE_NAME:dust:NP] #Again, changing the name
[TISSUE_MATERIAL:LOCAL_CREATURE_MAT:DUST] #Telling it to look for the "DUST" mat instead of "FLAME"
We now apply them to your creature. There's no need for STANDARD_MATERIALS or VERTEBRATE_TISSUE_LAYERS as we'll be applying our own materials and tissues. We can apply the dust layer to everything.
...
[BIOME:NOT_FREEZING]
[BODY:HUMANOID:2EYES:2EARS:NOSE:2LUNGS:HEART:GUTS:ORGANS:HUMANOID_JOINTS:THROAT:NECK:SPINE:BRAIN:SKILL:5FINGERS:5TOES:MOUTH:FACIAL_FEATURES:TEETH:RIBCAGE]
[USE_MATERIAL_TEMPLATE:DUST:FLAME_TEMPLATE]
[STATE_COLOR:GAS:GRAY]
[STATE_NAME:GAS:dust]
[STATE_ADJ:GAS:dust]
[MAT_FIXED_TEMP:NONE]
[DISPLAY_COLOR:7:0:0]
[USE_TISSUE_TEMPLATE:DUST:FLAME_TEMPLATE]
[TISSUE_NAME:dust:NP]
[TISSUE_MATERIAL:LOCAL_CREATURE_MAT:DUST]
[TISSUE_LAYER:BY_CATEGORY:ALL:DUST]
[BODY_SIZE:0:0:2000]
[BODY_SIZE:1:0:8000]
[BODY_SIZE:2:0:19500]
...
(Are these things supposed to be so tiny?)
Now the entire creature is made up of dust, which acts like a gas. Now we need to add the flames.
[USE_MATERIAL_TEMPLATE:FLAME:FLAME_TEMPLATE] #Designated as FLAME this time
[DISPLAY_COLOR:2:0:0] #Green flames, anyone?
[MAT_FIXED_TEMP:9870] #Fat starts taking cold damage at 9900
And the tissue:
[USE_TISSUE_TEMPLATE:FLAME:FLAME_TEMPLATE] #We don't need to change anything here.
Now we need to consider where the flames are going to go. Let's say we want them trailing off the dust. What we'll do here is add a layer on top of the previous layer, much like the way head hair and nails are handled in the dwarf entry.
...
[BIOME:NOT_FREEZING]
[BODY:HUMANOID:2EYES:2EARS:NOSE:2LUNGS:HEART:GUTS:ORGANS:HUMANOID_JOINTS:THROAT:NECK:SPINE:BRAIN:SKILL:5FINGERS:5TOES:MOUTH:FACIAL_FEATURES:TEETH:RIBCAGE]
[USE_MATERIAL_TEMPLATE:DUST:FLAME_TEMPLATE]
[STATE_COLOR:GAS:GRAY]
[STATE_NAME:GAS:dust]
[STATE_ADJ:GAS:dust]
[MAT_FIXED_TEMP:NONE]
[DISPLAY_COLOR:7:0:0]
[USE_TISSUE_TEMPLATE:DUST:FLAME_TEMPLATE]
[TISSUE_NAME:dust:NP]
[TISSUE_MATERIAL:LOCAL_CREATURE_MAT:DUST]
[TISSUE_LAYER:BY_CATEGORY:ALL:DUST]
[USE_MATERIAL_TEMPLATE:FLAME:FLAME_TEMPLATE]
[DISPLAY_COLOR:2:0:0]
[MAT_FIXED_TEMP:9870]
[USE_TISSUE_TEMPLATE:FLAME:FLAME_TEMPLATE]
[TISSUE_LAYER:BY_CATEGORY:ALL:FLAME:TOP]
[BODY_SIZE:0:0:2000]
[BODY_SIZE:1:0:8000]
[BODY_SIZE:2:0:19500]
...
Unless I've messed up, we now have a creature made out of dust, with cold (and green) flames trailing from the top of its body.
There are a few other things that you've missed, but I'll go over those once I know you don't have any questions on this.