When people and objects cross over between Earth and Bizarro Earth, one item that appears is the North Korean submarine that Clark rescued from sinking in the season premiere.
Bufotoxin is a moderately potent poison secreted in the skin of many anuran (the most terrestrial order of amphibians) amphibians, especially the typical toads (genus Bufo).
In the ending scene, Superman throws a Kryptonian Crystal in water and an island was created by that single crystal. That is what has already been shown in Superman Returns (2006), though it was a villain that created the island in that film.
Miracle Monday is the title of a Superman novel by Elliot S. Maggin published in 1981.
When Chrissy Beppo is broadcasting her message at the beginning, at 0:27, Taj Mahal at Agra, India is shown between this world's round yellow Sun and Bizzarro world's cube red Sun. Before that Eiffel tower and Burj Khalifa were shown.