Gatz

Gatz, known as Gaga (ガガ) in Japan, is the Servitor Unit for Mistress Yuna and protects her with his life. Gatz has a Reaverbot eye on his forehead and has the ability to transform into a large silver dragon-like Reaverbot and merge with machines.

History
In Mega Man Legends 2, Gatz uses his alternate form to transport Yuna and attacks the Sulphur-Bottom as a warning to make them return, but accidentally damages the engines and traps the Sulphur-Bottom in the storm of the Forbidden Island until Mega Man Volnutt stops it.

After the four keys to the Mother Lode were stolen by Sera, he separates Geetz from the Sulphur-Bottom and fights against him, but Geetz knocks him down. After Mega Man defeats Geetz, Gatz merges with the broken Shuttlepod in Calbania Island to repair and use it to reach Elysium with Yuna and Mega Man. Gatz reveals he has reservations about destroying the System, but will follow Yuna no matter what happens. Gatz tries to help Mega Man against Sera by attempting to invade her internal systems and sabotage her, but Sera discovers him and kills him by unknown means.

Trivia

 * In the Japanese version Yuna only calls Gatz as "Gā-chan" (ガーちゃん).