"The spiders have long since taken over these fields."
Restrictions: No Towers
Succeeded with one life using Valorius 5, Knuckles 5, Cobra 7, Sapphira 6, Freeze 7, Clarion 6, Healing Spring 6, Rally 3 and utilised video ad for extra slot for Thunderstorm 5.
My main hero was also equipped with Boots of Quantum Stride and Girdle of Pain. These boots provide a significant advantage as it is possible to target a stray foe instantaneously with the main hero.
It is probably also worth noting that with a sufficiently high level Rally, Healing Springs could be left out and replaced with another spell or hero since with each use of Rally all your troops receive some health including Clarion I believe.
Please check this link for detailed discussion on this level. If you have a problem winning other stages, try to search around the forum to find instructions!