I got a idea for this mod: Black dragons, They come out at night and stay in morning. Fly higher then wraiths and can me tamed like horses so this one is mount. And are neutral at day and aggressive at night so it's safer to tame them in the day and they Shoot fire at you and drop fire. And are made of 12 blocks and are 4 blocks high. I will try to draw a picture of what I mean of what it looks like. But in the mean time try working on it for 1.6.4
Dragons was already suggested. But I honestly think they're too big. It would be silly in Minecraft. The only thing I'm waiting for right now is the update so I can check out the new patch.....and hopefully a fix for the spinning whilst riding horses.