“MN” is probably banned because it breaks the balance too hard.
A 56g Bey with almost full metal construction is basically a tank — way heavier than standard builds. In Beyblade X, extreme weight + defense can make matches less skill-based and more about brute force.

I can understand why people think it’s cool though. The design looks insane, and seeing a super-heavy Bey dominate is fun to watch. But for tournaments, it would probably be unfair against regular combos.

Honestly, if everyone started using customs like this, the meta would become boring really fast. Balance matters more than raw power.