And just so you know, do NOT apply anything water-based directly to any MAC eyeshadows. They're not designed to be used wet, so they get really hard if you wet them, and you'll pretty much never be able to get it out again. Like browneyedbaby said, you should just mess around and see what you prefer in terms of mixing the shadow with a mixing medium. I have a petri dish, and I normally just scrape a little bit of the shadow into it with a craft knife, then add a teeny bit of mixing medium and mix it up. The most important thing to remember though, is not to press a wet brush directly to the shadow, it will ruin it. However, it is okay to do this with Mineralize products, because they are baked and formulated differently.
Also, just so you know, you can make your own homemade mixing medium by mixing three parts water with one part glycerin (you can find it in the first aid aisle at a drugstore or Wal-Mart for like $3). I just bought one of those $2 MAC travel bottles and I keep it in there.