Survival mode
In most fighting games there is a survival mode. You choose a character and you fights as many enemies in a row as you can.
I would really like something like this in MCOC. Maybe it can be on a weekly basis where you can get milestones based on the amount of fights you won. In increments of 5 or 10. Rewards could be focused on catalysts and you could have 3 modes, easy, medium and hard.
Easy- Oponents PI are about the same as the first 3-4 rounds in arena
Medium- opponents PI are about the same as your character
Hard- Opponents PI are somewhat higher than your character, like rounds 10-15 in arena if you do not face thanos teams.
When you use a champion they go on cooldown, and they will only be available next round/week.
Every time you try with a new champ you reset your progress, but if you have reached the milestone of 20 fights before you will have to do 25 fights before you can get any more rewards.
Rewards could be stuctured as followed, example based in a thronebreaker summoner:
Easy- t4b and t1a
Medium- t4cc and t2a
Hard- t5b and some fragments of t5cc
For example.
Either your champ would constantly continue with the health of the previous fight, or they could heal for 10-20% each time you get a reward milestone. So every 5-10 fights.
I would really enjoy a mode like this, especially if there could be some form of gold/battlechips/units along with the other rewards.