Hi, first time here. I decided to post since I couldn't find an answer on the Compendium's analysis section.
Anyway, when the party is assaulting the Black Omen, how is it possible for a Lavos spawn to be sent from 2300 AD to 12'000 BC? It's doesn't make sense, because it shouldn't be possible for this Lavos spawn to even exist! From the point of view of 2300 AD, whatever came before is past and has already happened, including the party's invading the Omen in 12'000 BC, which immediately leads to the party defeating Lavos in 1999 AD. Both things, from the point of view of 2300 AD, have already happened, so the future should be pristine, not ruined, and Lavos spawns shouldn't even exist in the first place.
Think about it: Suppose it's 12'000 BC and the party is assaulting the Black Omen when Queen Zeal summons a Lavos spawn. Years later, in ruined 2300, AD a Lavos spawn is just chilling when a Gate opens, with Queen Zeal commanding it to warp to 12'000 BC. But before entering it, the spawn decides to look back at the timeline. It sees the party arriving at the Black Omen...but does it see itself arriving? No, because things only happen when they happen; until the spawn enters the Gate, we are still in a timeline in which the spawn has never arrived in 12'000 BC.
Then, what happens next? It sees the party continuing their assault on the Omen, it sees Queen Zeal being defeated, it sees the party falling into the Omen Gate to 1999 AD. Because the spawn is in 2300 AD, events in 1999 AD are in its relative past, so it does see the party arriving in 1999 from the Omen Gate, it sees Lavos erupting, it sees Lavos being defeated by the party...at which point the Lavos spawn thinks "Oh crap!" and vanishes. It never gets the chance to travel to 12'000 BC!
The only explanation I can think of is dramatic coincidence. Basically, while the party is out doing sidequests but before Lavos is defeated, Queen Zeal, hoping to improve the Black Omen's defences, summons a Lavos spawn from the future. This works because the future is still ruined and it isn't far-fetched to think she would enlist extra-temporal help to defend the Omen. From now on, the spawn's appearance in 12'000 BC is protected by time traveller's immunity regardless of the state of the future. The problem is, because she's proactively summoning the spawn rather than reacting against the party's assault, the specific chamber and moment she summons the Lavos spawn are essentially arbitrary. Yet the party encounter the spawn at precisely the right place at precisely the right time to see it just coming out of the Gate, a huge coincidence for which the only explanation is "rule of drama".
