Its funny that in the real world its just called Yugioh, even the official name is Yugioh. But in the story its called Duel Monsters. If you tried to call the real game Duel Monsters you'd be made fun of.
@fillertrack and yet
annnd yeettt
there really was a card game called Duel Masters, AND an Anime made of it, that was not in any way affiliated with YGO. Yet it's blatantly a shameless ripoff of YGO, and has a blatantly similar name.
@Nine actually Duel Masters was a rip off of Magic the Gathering. Or it was an ad for Magic in Japan. It was first a manga where they played MtG. But then they made a separate card game with some MtG mechanics to sell to younger kids. It was developed by Wizards even.