Trinicus is Mint's dad
Arche is 13 in half-elf yearsAs in, she's in her thirties or more in human years. Physiologically prepubescent, but due to her half-human blood, she's aged mentally at a human rate. Hence her rather... adult personality, and not being a virgin, and so on.
Sometime between Symphonia and Phantasia, Undine and Celcius fused togetherThis would offer an explanation as to what happened to Celcius, and why she isn't seen in Phantasia.
The Lester and Morrison families team up behind the scenes in the altered timeline.They need to make sure no one messes up the timeline they worked so hard to create. Using Klarth and Edward's memoirs they create the seals on the mausoleum and keep an eye on things to make sure that the Heroes of Eternity can do their job without interference once they arrive in the future(s). This probably also makes Klarth responsible for the seals on the blades of Ice and Fire, since they sort of made a Stable Time Loop with the Eternal Sword... Which means you can blame him for the fight with Fen Beast.
The GBA version is a retelling of the legend.Not the original story itself, but rather, someone, somewhere, at some point in the future, telling someone else of the legend of the heroes who mastered time itself to defeat Dhaos. If it's been long enough, this would explain the discrepancy in the names: people no longer remember what they were really called.
Dhaos and Cress are somehow related.They both have blond hair, a red headband, and a red/orange cloak/cape. If they aren't actually related, they were meant to show their similarities.
Dhaos knows Kratos.Kratos was Dhaos's mentor.