So I think that if we were to get another Mario and Sonic crossover, it should be an RPG. Specifically, a Mario and Luigi game
In the game, Mario and Luigi would play the same as Brothership but Sonic would have a different set of attacks. Instead of stomp, he would have homing attack and instead of hammer, he would have spindash.
I imagine one of the bros attacks would involve Sonic grabbing both Mario and Luigi by the arms and running behind the enemy and throwing the bros at the enemy and at the end, he would perform the final blow. Perhaps another one where Sonic, Mario, and Luigi use the chaos emeralds, going super, and use the enemy like a tennis ball and keep hitting the enemy back towards one of them. The final blow would have all three of them sending the enemy back to earth before landing and transforming back.
Not sure what the story would be but I think it would be a nice idea