Power Yoga is a dynamic practise that challenges the body to build strength and endurance through a flowing sequence of poses. These classes are as challenging as you want them to be. I say this because while you are most often given options during a class to work from easy to hard, you have the option to push your edge or faff around and nap. It actually doesn't matter either way because the key is to listen to the voice of your body when it's saying to you, "you can hold that longer or sit this one out".
You will also find power yoga challenging if you have never practised yoga before, you have strength and endurance in other ways (like gym strength or running endurance) or your mindset is off-line. None of that matters either, if it means anything to you, it's something you can ponder on while you're sipping your magnesium before bed.
Listen, life is serious enough without making it any harder. Do it or don't to whatever degree you feel like on the day, it's as simple as that.
Mixed Movement is fun, energising, dynamic, challenging and broken down into understandable bites. It is a blend of yoga, animal movements, martial arts, medical Qigong and energy medicine. It has all the challenges of Power Yoga, it has some yoga movements within it and all the questions of your resistance, but it is not a pure yoga class.