Added mustard powder to my deep protein mix today. Forgot my vanilla mint chai rinse but will do it before my moisturizing deep conditioning in a minute... The mustard powder heated up my scalp so the mint should have a nice cooling down effect.
Edit: One thing I will say about this mustard powder is that you don't want to leave it on you head for an hour or more unless you are using it on your scalp ONLY. It is really drying as the recipe
cynd posted in the steaming thread, and it started to "dred" my hair just a little like a protein treatment does. Also, unless you completely dissolve the powder in some kind of liquid, you will have to wash out the little particles (I co-washed them out). I had this experience with fenugreek seeds and slippery elm powder and I just blow dried them out when they were in my hair so that works too.
The mint did have a cooling effect so it countered the mustard.