The Iron Giant and RX-78-2 Gundam take Ultraman's role in the Ready Player One movie. This was presumably due to the rights dispute between Chaiyo and Tsupro, preventing WB from gaining the rights for the character. (2018)
Most Extreme Elimination Challenge (a re-edited americanized ver of Takeshi's castle) features an episode with multiple Ultra kaijus, including a renamed zetton called Queerwig who "climbs into the ears of sleeping children and turns them into gay teens" (2003)
The orbs on Kaiser Belial's cloak are meant to represent the color timers of fallen Ultras. This is said to be inspired by the Yautja species' tendency to wear the skulls of their victims. (2010)
Yuriko Hishimi (Anne from Ultraseven) baked a cake marking the 50th anniversary of episode 12 of Ultraseven. she attempted to start a campaign to get the episode unbanned in memory of director Akio Jissoji, but unfortunately it didn't go anywhere (2017)
The Power of Baradhi is first mentioned in episode 7 of Ultraman '66. Eventually becoming integral to Ultraman Noa, 44 years later in Revenge of Belial (1966)
The Seven episode Nightmare on 4th planet was initially turned down by the network because it had no monster, so in response Akio Jissoji wrote an episode which had every Ultra monster and alien introduced to that point, making the network back down (1968)