>>25249888>>25249924>>25249942The final boss is called Dark Matter; it's basically Bittercold in a lot of ways if you've played Gates
Nuzleaf is being mind-controlled by Dark Matter and actually winds up being a major villain later on
Espurr is hinted at coming under Dark Matter's control as well but she was Merely Pretending[tm] and shows up later to save the day
At one point you get access to five different continents, including the newly christened Grass Continent where Explorers took place, but you can't actually return to Treasure Town
Your partner is the one who disappears at the end instead of the hero; it's revealed before you go to get them back that they've been reincarnated from a Mew who lived long ago and teamed up with the player when they were a human at that time.
There's nothing to do after rescuing your partner unless you're an avid completionist who wants to fill out every single connection in the connection orb