Sgt. Frog Episode 200: Keroro, Uru Has Come!
Episode 200 of 358 of Sgt. Frog, aired February 23, 2008, 25 minutes. Available with English subtitles and dub where released.
Episode summary
After hearing about Leap Day, Keroro gets terrified that a giant monster named Uruu will come to beat all the invaders. Thanks to his terror, the monster actually appears! Source: crunchyroll