My sister is the one who introduced me to this mask and oh BOY is it intense! I use this when my skin is REALLY not cooperating, like when it's extra oily, red, or breaking out. You mix the powder with apple cider vinegar and leave on for 10-30 minutes, depending on how sensitive your skin is. IT TINGLES. A LOT. When you wash it off, you'll look like you were out in the sun without sunscreen on — but the initial redness only last about 30 minutes. You're left with clear, smooth, and deeply invigorated skin. Personally, I don't use this more than once a week because of how intense it is, but I love it.
Get it from Amazon for $10.95.