So, I've been seeing a lot of theories about the possible plot of Sonic 4, more specifically about the Time Stones, time travel and Amy maybe coming from the future. But what if, hear me out! what if Amy came from the past?
Amy originally met Sonic because her Tarot cards foretold her destiny on Little Planet, so she traveled there to meet her destiny and she did, so I see Movie Amy as perfectly capable of time traveling for similar reasons (or to help someone in need, that's also a very Amy thing to do).
Maybe, 50 years in the past? 👀 Imagine she knows Shadow? (Maybe she rescued Sonic initially mistaking him for Shadow). Shadow said he doesn't remember anything about his origins but him losing his memory after crashing on Earth is nothing new in the franchise. Maybe the circumstances that sent Shadow to Earth were the same ones that made Amy to travel to the future?
I know it's all unlikely but you have to admit it would be a good way to include these little details we missed out due to Amy's exclusion from the SA2 plot in Sonic 3, with a unique twist like everything else so far in the movies.