>>31850297Well OP, there are a few reasons for this.
>1. It's a Legendary.In the game code, Celesteela and the rest of the UBs are classified as "sublegendaries," the same as Pokemon like Moltres, Registeel, Azelf, etc. Legendary Pokemon often have very odd designs, especially from gen 3 onward, and do not look like traditional "Pokemon." For example, see Arceus, Volcanion, Giratina, Deoxys, etc.
>2. They're from a different world.They are said to be Pokemon, but from a different world (Ultra Space). Thus, it makes sense that Pokemon in that alternate world would have different designs from Pokemon of the initial world (similar to Deoxys, but not explicitly space aliens).