>>50024518I had thought of a parallel system sorta like wizards101. You free roam normally (this can be the normal PMD grid based movement), but there is a parallel process for combat. If player 1 is in combat, there is a combat radius. If player 2 enters this combat radius, then their combat synchronizes, meaning it will wait for input from both of them. So it'll slow down when you are together, but you want to search separately you can do so without being punished if the other person starts fighting.
But after looking up the game play for rumble blast, that honestly looks like it'd fit the niche pretty well. You could adjust the movement to be grid based, and boom, co-op PMD.