Libabeel is one of the legendary Pokemon from Naljo.
Libabeel can be obtained as early as you receive surf, being located in Acqua Mines. From the room where you met Larvitar, surf left for a little while then surf up to find a cave entrance. Go up 2 Ladders and that's where you will encounter Libabeel. Upon being defeated, and or flee from battle, Libabeel will return upon defeating the Naljo Elite 4.