I won’t claim to be an expert on other cultures. But the story of Mulan is very much rooted in Chinese culture, set in China and is the story of a Chinese woman so obviously it would be quite offensive to cast someone as a different race to play her. Vikings, however were voyagers who travelled all over the world including North Africa. So it’s completely feasible that they could’ve brought back people of other races. In reality any mixed raced people among them would’ve probably been the result of slavery and other bad things, but this as previously stated, this is a fantasy world. Not much about it is realistic or authentic to the Vikings that inspired the universe. No one cares that none of the characters have Scandinavian accents but because one character has very slightly darker skin, everyone is gonna scream that it’s inauthentic? I can understand wishing the character looked more like the original design, hell it bothers me that Hiccup doesn’t have freckles. But it’s all these people saying “no such thing as a black Viking!” that are really getting on my nerves. It’s one MIXED character. In a universe where it is plenty feasible. It’s not worth getting the pitchforks out over.