Very nice. I can easily see Harry slowly getting corrupted by the power of the Overlord (wonderful games) as he grows more and more desperate to defeat Voldemort, that by the time that happens, Harry is even more evil than Voldemort is. And one thing about evil is, people who are evil rarely think of themselves as evil. They see their actions as a means to a glorious or noble end. They grow disconnected to the world around them.
As for the blue mounts, I think it should be something amphibious. Some kind of snapping turtle maybe. Rolling around in their shells behind the other minions, reviving them in passing.
As for the black minions, I like. Maybe their mounts could be something like Skaven from Warhammer, disgusting mutated ratlike creatures in the sewers. Skaven are remarkably cunning and dangerous, but I wouldn't think of them as particularly smart. Smart as the average minion at any rate.
Will Harry like have one or two mistresses from every house in Hogwarts?
Author's response
Thanks for the reviews. As for the mistresses, the current plan includes Hermione, Luna, and Fleur. Might change as the story grows, though.