Just got this email a couple hours ago, and I thought I'd put up here and pass it along in case you hadn't seen it yet. Check it out!
Yup! A free level and some fun stuff in your bags if you type in the super hero squad free code "GOODIES"! WOOT!
After redeeming the code, log in and head to your backpack to use it.
Just don't waste the heroup potion on the early levels of your hero! ;)