https://www.nintendo.com/games/detail/legend-of-mana-switch/
This was an underrated gem from the ps1 era. I know its older brother gets a lot of love but this game was a real masterpiece for allowing the player to explore in their own way.
Ign recently reviewed it as a 7 but I have some qualms with the review. It praises the art work but complains of no direction and lack of difficulty.
The game is wide open allowing multiple play throughs and a ridiculous amount of variety. And on top of that there is new game plus mode which the reviewer must not have known that can increase the difficulty level.
Eitherway if your looking for a truly unique co-op experience, give this one a try.