Phantom Monster Agon, Atomic Dragon (1968) dir. Norio Mine Fuminori Ohashi

Giant monster, spawned by atomic explosions, emerges from the sea and wreaks havoc, leaving scientists trying to figure out how to destroy it. Originally a Japanese TV series made in 1964 and aired on Fuji TV in 1968, the four episodes were stitched together and released by Toho as a feature film in the mid 1990s. In Japanese, with no subtitles (and they re not really needed for kaiju lovers).