Personally, the Emeralds break most matches. Sometimes, players completely ignore the fight and search for the Emeralds, becoming easy targets. And if someone gets 6 emeralds, other players can just take the last one and hide, effectively trolling the player with the other 6. But, it's a somewhat balanced mechanic, and just needs a bit of work. However, the item that's truly is broken is the Rail Ring. Give this to anyone with decent aim, that player quickly becomes the winning player. Just like the Blue Shell in Mario Kart 8, the Rail Ring needs a hard counter, and quite a bit of tweaking. Anyways, 2.2 look great- I can't wait.
And about a MVM style mode, that would be a blast. [Pun Intended. Call the mode Robo Blast.]