You will find no Marvel walk-around characters at Universal Studios Hollywood. Not since Jan 1st, 2008.
At Islands of Adventure, you will find them in Marvel Superhero Island. I don't think there are any at the Studios park in Florida.
Currently raising funds for the AMAZING Give Kids The World for their annual Coasting for Kids event. Any amount would go a long way in helping a family enjoy an amazing Orlando vacation. You can donate on my page.