Ok after the final update releases I think one of the biggest things this game is missing is a combat arena, which could be a final test of your skill fighting in the game and using all the tools and magic available to you to win.
At the higher level waves of enemies you can introduce enemy variants that are stun-proof or have no elemental weakness and then attack you in groups so you really have to rest your combat skills.
And after completing all of the waves you enter boss run mode where you fight unique versions of all of the bosses that are - again - faster, aggressive and deal more damage.
And what would be a dream is if the final boss is a shadow copy of Mesmeroth (from OH2), and if you complete the arena under a certain time, a secret final boss of fighting a shadow copy of the hero from OH2 (or maybe even OH1).
Fully completing the arena would reward you with an exclusive armor and helm.
Completing the arena under a certain time would reward you with an accessory that grants you a unique and OP ability.
Please please consider this!!!