The Creeps never rest! Take your heroes through 15 fights across 5 regions of the city to keep them in check. Each battle you win earns you gold, and each region rewards City Watch Tokens. Plan ahead! Heroes retain their HP and energy from previous fights, but KO'ed heroes remain KO'ed until you reset the Watch.
Clear the city of Creeps on easy to unlock medium difficult - HP and energy won't regenerate, but you get extra rewards. Clear medium difficulty to unlock hard difficulty - HP and energy won't regenerate and all enemies will be buffed with a Weekly Ward, but you get more bonus rewards and Epic Keys to access Epic Mode.
To unlock Epic Mode, you need to own at least one hero with a red rank skill, and Epic Keys. Only red rarity heroes can be used in Epic Mode. Rewards for this mode grant Red Skill Chips, which are needed to unlock and level up red skills. Red Skill Chips are dropped for heroes that win battles in that region. Red Skill Chips do not drop for mercenaries on your team. Epic Mode has both daily and weekly wards.
If your team power is so high that matchmaking can’t find someone tough enough for you, it will pick an opponent and increase the level of their heroes. This means you may see someone with a team level lower than the level of the heroes you're fighting.