User blog comment:SsVivid/What I Learned From TMF/@comment-11555902-20140603050719/@comment-1962440-20140603082247

He didn't mix creatures to create them, he selectively bred them from a single species. See that he refers to them as breeds, as one might a dog(in his memories). I believe that Zarador also mentions this post-quest as something Bandos told him, but I'm not online to check.

Bandos didn't "stay pure" he was the last of his kind and never bred with anyone, it's debatable whether gods can breed with mortals. We've known since The Bird and the Beast(or before?) that Bandos wasn't from Yu'buisk. Bandos wreaking havoc is hardly a surprise to anyone. The Dorgeshuun tribe was only "inferior" because they rebelled, something known for years. He sure did invest a lot of power into making her succeed if he thought she would fail.