Nazo no kyôryû kichi

This is most definitely one of the most famous episodes of the original Ultraman and it's a pretty fun one also. It starts off with a rather routine operation for the Science Patrol only to run into the scheme of an archetypical mad scientist and a last minute twist ending. Of course, what really is this episode's claim to fame is the appearance of Godzilla in a pretty conspicuous disguise. Given the connections Tsuburaya had with Toho early no it's a real treat to see his two famous creations face off. They definetly knew what they were doing when Ultraman tears of Jirahs' frill and pays respect to his fallen foe.