"Attack of the Fierce Frogs" is the thirty third episode of the lion series of Voltron: Defender of the Universe.
Plot Summary
Haggar creates many Miniature-Robeasts disguised as tadpoles to invade Arus. They will thrive in water which Haggar explains to Prince Lotor is where Voltron does not fight well.
On Arus, Pdige comes across two siblings while out on patrol. They explain that they're collecting some tadpoles. Pidge helps the children get them home, where he meets their parents. Pidge learns their father is a ship captain as he leaves to go to his job. Pidge then takes some of the tadpoles for himself back to the castle.
That night, a group of mutant amphibian-like creatures attack the ship commanded by the father of the children Pidge befriended. Though they easily destroy the ones in the castle, the Voltron Force's attempt to destroy those out at sea and everywhere else on Arus proves more than difficult. Then a larger robot arrives as well, and damages Voltron. Working together, the team is able to overcome the Robeast even whilst at a disadvantage so deep underwater.