There's also the codes TEAMCAPMB and TEAMIRONMANMB for the corresponding Mystery Box, which is guaranteed to contain either a random costume or a random hero, as well as a visual artifact of the character's logo, on top of other goodies (which range from common items like boosts to rare items like the corresponding character in their Civil War costume as a Team-up). Like the character codes, you can only choose one.
Apparently, the mystery box was supposed to come with the character, but they messed up and forgot to include them, so they just turned them into separate codes.
Edit: They extended the time to redeem these codes from just the weekend to the entire month.