This is the first appearance of Professor Souichi Tomoe and Kaolinite. In addition, Sailor Neptune and Sailor Neptune also appear for the first time in this episode, albeit as silhouettes.
Deep Submerge and World Shaking are used for the first time, though they would not be named until A Wonderful Beautiful Boy? The Secret of Haruka Tenoh (1994) - two episodes later.
This episode marked one of the rare occurrences that a Sailor Guardian (other than Sailor Moon) defeated the enemy-of-the-day, in this case Sailor Uranus and Neptune, who defeated Mikuji with World Shaking and Deep Submerge.
This is the Season 3 Premiere