I stopped attending local tournaments when they allowed Yugioh to be used in the mix.
Were they forcing you to buy YGO?
I doubt it. But if you play the game to pit Marvel characters against Marvel characters, then pitting them against Yu-Gi-Oh may not be interesting.
Can't get past the YGO theme?
Now you can in 4 easy steps.
1 - Mock up some fancy Marvel art, and put a fancy Marvel name on it.
2 - Cut out the fancy art
3 - Match it to a suitable replacement
4 - Sleeve it.
There you go, now it's Marvel, and you can play it!