The Forgotten Titan
The ever-expanding web of mystery that Monarch: Legacy of Monsters dangled an interesting thread in the eighth episode of season 1 by mentioning a Titan that had seemingly been forgotten within the Monsterverse. Episode 8 contained a number of big reveals about the Monsterverse, including its massive Hollow Earth twist. The revelations of episode 8 could help explain why one seemingly significant Titan hasn't been mentioned in more than five years.
Monarch Sciences Map
The 1950s timeline in Monarch: Legacy of Monsters has largely been about how Monarch began, and how it was eventually legitimized by the American government. In episode 8, Keiko tries to help Bill turn his disorganized field notes into a coherent report on Titan sightings around the world that he can present to General Puckett and ensure that Monarch continues to be funded. It was during that conversation that the two scientists made reference to a Titan that was first teased in the promotional materials for Godzilla: King of the Monsters.
Bill Randa and Keiko in Monarch Legacy of Monsters
As Keiko tries to interpret Bill's sloppy field notes in Monarch: Legacy of Monsters episode 8, she claims that they can start by eliminating any Titan sightings with no real evidence, and specifically mentions a Titan that Bill believes is in Siberia. That Titan was actually teased way back in 2018 on the Monarch website, which was used to provide Monsterverse clues and build anticipation for Godzilla: King of the Monsters. The map is gone, but the discussion can still be found in places like Reddit. However, when Dr. Mark Russell is shown the map in Godzilla: King of the Monsters, the Siberian Titan is nowhere to be found.
The Disappearance and Reappearance
Despite Bill Randa's belief in its existence, it may have never been confirmed by Monarch. At the time, the disappearance of the Siberian Titan was largely dismissed as a simple change in direction or even an oversight, but with it resurfacing in Monarch: Legacy of Monsters, it appears that there was, in fact, a Titan there. The reason it may have disappeared from the map used in Godzilla: King of the Monsters could simply be that Monarch never fully confirmed its existence, or at least didn't have the ability to locate/monitor it with a full outpost. That suggests that their research never got much further than Bill's field notes originally did.
The evidence for the Siberian Titan was never strong in the first place. While Bill claims he found three independent sources, Keiko dismissed them based on their illegitimacy. She describes them as 'two drunk, one blind', indicating that their reports were far from reliable. However, the Titan being mentioned twice in Monsterverse content is no coincidence--it likely means there really was a Titan there at some point. Its disappearance can be explained rather simply: it entered a portal and disappeared into the Hollow Earth for many years, or exited elsewhere and is actually one of the 17 known monsters from Godzilla: King of the Monsters.
The Future of Monarch: Legacy of Monsters
One of the unique features of Monarch: Legacy of Monsters is the two parallel timelines playing out simultaneously as the show progresses. It's fair to assume that the second season of the show will continue to use that distinct method of story-telling once it is confirmed, given its strong viewership numbers. If it does follow a similar setup, the Siberian Titan could make an appearance in the past timeline as Keiko Miura, Bill Randa, and Lee Shaw continue to expand Monarch's scope. With additional funding, they can expand their team and investigate more of the Titan sightings that have occurred around the globe.
Season 1 also links the past to the present, with the Randa children following in both their father's and grandparents' footsteps as they dive deeper into Monarch's secrets. It's possible that the Siberian Titan appears not only in the past timeline but in the present one as well, especially if its presence goes unnoticed in the years between them. That seems likely due to its omission from Monarch's map of 17 known Titans from Godzilla: King of the Monsters. As the mystery of Monarch: Legacy of Monsters has progressed, no information can be dismissed, and it seems likely that the Siberian Titan will make an appearance sooner or later.