If the精灵 Star Baby can fly, then the精灵 would be really invincible.
(Note: "精灵" is repeated in the sentence and might refer to a specific character or concept. Depending on context, "精灵" could be translated as "fairy," "sprite," or "elf." If it's a proper name, it should remain consistent or be transliterated.)
A more polished translation might be:
"If the Star Baby fairy can fly, then the fairy would truly be unstoppable."