I like it too, but WildEep made a really good point to me on IRC. He suggested we use Pokéball because of Tyranitar's large amount of good egg moves. If we use a special ball, it gives away that the Tyranitar doesn't have DD/Curse/Pursuit/etc. On most Pokes, I'd go for ball over stuff like that, but I think on a Tyranitar it could be important.