Does going to a graduate school with less prestige than your undergraduate school hurt you? I am trying to decided whether pursing a Master's in Computer Science will make me more competitive for a job designing video games. I went to a prestigious undergraduate school and finished strongly. The graduate schools which offer Master's programs with concentrations in video game design are less prestigious than my undergraduate school.

The average starting salary with a graduate degree from one of them is actually $30k less than my starting salary with just an undergraduate degree.

If I attend a less prestigious graduate school, will that cancel out my undergraduate degree? Could I end up making less money with my graduate degree from one of these less prestigious schools? Will employers make the false assumption that I attended a lesser graduate school because I did poorly as an undergraduate?
Edited heavily based on further information provided by OP
If you are going into industry, or pursuing a Master's, it may hurt you in the short term
A Master's degree is mostly course work. It's too short for you to create a body of work that stands on its own. The quality of the courses largely determines, consequently, the quality of the Master's. Prospective employers may use an institution's reputation as a heuristic/proxy for the quality teaching.
Attending a less prestigious institution will make it more difficult to get interviews. Not being able to attend the bigger names also means you miss out on their alumni networks.
Create a compensatory professional network that overcomes these limitations. Most Master's in CS programs have a semester-long project. Make an impressive project and shop it around. This is a good way to build rapport with potential employers.