The key to all challenges is the Shield spell, it makes all units immune to damage AND knockback for 20 seconds on level 5. While in Epic War 3 you need to wait to cooldown, here you can spam Shield as long as you have mana (you have 400 with level 5 altar). No matter how strong your opponents are (Black goblin, Big Bang cart, Lord Baal, Super Angel), spam Shield and you can eventually win.
If you need more cash to buy upgrades, it is better to farm lower level areas: The gold drop at lower levels isn't much different from the higher leves.
My method to get gold souls on all levels: 1. Start off with Cursed Blocks on every other line. 2. Once you get 3 souls build a new one on top. 3. When you get another 3 souls replace one Cursed Block with Magma Block. 4. Stack up as many Magma Blocks as you can. Practice a bit and you can get all gold souls with a few tries. Vote up to keep it alive.
Tips for Zodiac Memory (the optional superboss): Since one of his spells keep your hitpoints at 1 for a while, and there is no way removing it, if he uses it most likely you will die. The point is to kill it before it even have a chance to use that spell. The best bet is to throw Golden Apple's (obtained from Virgo), they take around 25% HP off the boss. Also, having a super damaging beast (say, Tiamat's breath attack) also helps inflicting heavy damage in a short time. Vote up to keep it alive.
An alternate (Ice) build to get the hard badge:
Spend 15 points on Ice skill tree, skipping Deadly Nova and Blizzard and get Frostbite to only 1/3. The remaining 13 points are used in Divine skill tree: fully upgrade Holy Grace, Swift Retribution, Miracle Healing, Holy Wrath and Chosen One.
In this build you can shoot Ice bolts like machine gun, and uses Freezing Nova to temporily halt monsters, then use Sparks of Life can keep yourself alive. Vote also to keep it alive.
 "Epic War 2"){kind=icon}
 "Epic War 4"){kind=icon}
 "Toxers"){kind=icon}
 "Neon Race"){kind=icon}
 "GrindQuest"){kind=icon}
 "Demons Took My Daughter"){kind=icon}
 "Wings of Genesis"){kind=icon}
 "Wizard's Run"){kind=icon}
 "The Trader of Stories"){kind=icon}
 "Indestruct2Tank"){kind=icon}
 "Epic Coaster"){kind=icon}