Tissues aren't what you're looking for; they don't control material properies (which is, naturally, the realm of materials). If you want, you can just point ot the "flame" material template (the same way the fire man does) and adjust its properties within the creature entry. Example:
[USE_MATERIAL_TEMPLATE:FLAME:FLAME_TEMPLATE] #We'll keep the internal material name as "FLAME" for now as that's what the tissue template looks for. You could change it, but that'd mean an extra line later on.
[STATE_COLOR:ALL:BLACK]
[STATE_NAME:ALL:shadow]
[STATE_ADJ:ALL:shadow]
[DISPLAY_COLOR:0:0:0] #This is pure black and will show up weirdly (just an empty tile). Personally, I like this, but you can change it to 0:0:1 to make the foreground element lighter
#I'm not entirely sure what to do with some of these values. On the one hand, you want the shadow to behave a bit like a liquid. On the other, doing that will probably break its combat effectiveness. I've set the strain values to that of blood for now, so you should have a hard time "breaking" it.
[IMPACT_YIELD:602000]
[IMPACT_FRACTURE:843500]
[IMPACT_STRAIN_AT_YIELD:10]
[COMPRESSIVE_YIELD:602000]
[COMPRESSIVE_FRACTURE:843500]
[COMPRESSIVE_STRAIN_AT_YIELD:10]
[TENSILE_YIELD:172000]
[TENSILE_FRACTURE:241000]
[TENSILE_STRAIN_AT_YIELD:10]
[TORSION_YIELD:172000]
[TORSION_FRACTURE:241000]
[TORSION_STRAIN_AT_YIELD:10]
[SHEAR_YIELD:172000]
[SHEAR_FRACTURE:241000]
[SHEAR_STRAIN_AT_YIELD:10]
[BENDING_YIELD:172000]
[BENDING_FRACTURE:241000]
[BENDING_STRAIN_AT_YIELD:10]
[MAX_EDGE:10000]
[USE_TISSUE_TEMPLATE:STRONGSHADOW:FLAME_TEMPLATE] #Unlike the material, the identifier here is only used in designations (and perhaps some creature variation templates/detail plans/etc). So if you're OCD about this as I am, you can change it.
[TISSUE_NAME:shadow:NP]
[TISSUE_MAT_STATE:LIQUID] #Fire men have this as "gas" but I think I'll change it, if only for the purpose of using you and your investment of time/effort as a gueina pig.
Then:
[TISSUE_LAYER:BY_CATEGORY(/BY_TOKEN/BY_TYPE):(bodypart category/token/type):STRONGSHADOW]
That'll do for the bronze-strength bits. For the rest you could just copy blood or something, but then it'd be hilariously weak. I suggest you instead use the bronze-strength-shadow for the entire body, which can be done via
[TISSUE_LAYER:BY_CATEGORY:ALL:STRONGSHADOW]
The mask thing is surprisingly tricky. You'll be able to make one via the ITEMCORPSE token, but you'll never be able to use it (due to a bug armour and clothing produced via ITEMCORPSE always comes out at some inane size). If you'd still like to try it, this should work:
[ITEMCORPSE:HELM:ITEM_HELM_MASK:BRONZE:NO_RACEGLOSS]
Evaporation is a bit... ehh. You'll want to somehow make it boil at underground temperature, but then you'd have to get rid of FIXED_TEMP, and even then the creature would just boil away/be in a constant boiling state/etc.. I can't think of a way of getting it to work properly.