Is is possible to have sorin just enter a "limit break" mode and jump through the portal and fight off any reptites that merge with it? He can then appear in a forest all wrecked (think robo after fiona), still protecting the dragon tooth?
That wouldn't be possible as Sorin is a human with cyborg implants, rather than a complete robot. Mmh, the Dragon Tooth is connected to the void, so we could perhaps have Sorin use it to remain as a ghost to protect it (a kind of throwback to the scrapped Valle Crimse ghost knight from the sidequest thread I guess). But is it...believable? I mean, a cyborg ghost living for 62 million years...
Concerning the StrongArm, what's curious is that Norris says it was "in development in Porre", but it was also "excavated near an ancient ruin" according to Luccia and destroyed when Norris "caused the explosion in the lab". Kinda hard to reconcile these statements, though I guess different things could have happened in the two different dimensions. For Sorin, I tried thinking about a solution involving our own Porre Lab, which would fit all three statements (Porre excavates Sorin, tries to repair him, before the party takes him back to Chronopolis), but that can't be as I would be mistaking Norris for William.
Perhaps we can just have Chronopolis excavate the Dragon Tooth in 2,305 A.D. (offscreen, during Marle's Antaeus chapter), thanks to Crono/Glenn/Magus's report of their adventure in Prehistory. They would simply repair the Tooth, and would have found the cybernetic components of Sorin's dead body too, including his arm. That only partially explains the StrongArm but I guess there are enough theories out there for the "in development in Porre" bit (this could be something that happens only after the Time Crash of CC).
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Time Egg uses:
1 Recover King Zeal
2 Arrival in Chronopolis (prologue)
3 Recover Notes
(4 Recover Dragon Tooth?)
5 Black Omen Trip
6 Final Dungeon
I like FaustWolf's idea of Belthasar (not Gaspar) using the FF anti-annihilation energy to "wish" King Zeal back (eh, that sounds like Abel wishing Elly from the Zohar in Xenogears). However, I think Zeality wanted to use the RD concept that the Frozen Flame + a Time Egg = control over space-time. Presumably using a Time Egg for that purpose won't shatter it, though RD is vague on this.
At most, we could lower the count to 4 Time Eggs if we don't use one for the Dragon Tooth and if the one used for the final dungeon is actually the one that was used to resurrect King Zeal. In Chapter 21 "Let us Part in Zealous Regret", King Zeal would simply leave his Time Egg to the party when he "invites" them into the Spire of Telos/DBT:
1 Recover King Zeal / Final Dungeon
2 Arrival in Chronopolis (prologue)
3 Recover Notes
4 Black Omen Trip