Myths of the Arena offers endless challenges for Heroes of any Soul rank, thanks to 4 different playing modes.

You can play Myths of the Arena as a co-op quest using the "Gods of the Arena" playing mode - a series of connected missions/challenges of increasing difficulty, ending in your fight with the Legends of the Arena, to win epic treasures.

But you can also use this expansion to enjoy using your Sword & Sorcery Heroes and Enemies using 3 bonus playing modes:

Lords of Endless Pain, where you find out how long can you hold your ground against an infinite horde of blood-thirsty enemies.
Kings of the Pit, where your challenge is to conquer the sacred altars and defend them.
Clash of the Heroes, where for the first time Heroes can fight against each other in duel - one vs. one, alone with a mercenary at youir side, or team vs. team.

Myths of the Arena can be played in the Ancient Chronicles campaign, but it is also completely compatible with Immortal Souls, and can be played in that campaign as well.