Yea the Dragon Heart is still there, I got it somewhere. Maybe through a quest, idk.

hmm...favorite combo?
My current all-Mage party...
Rune Mage - Good damages and skills.
Druid - becoming my favorite thanks to their spread damages. First and second skills are okish, third one is useless.
Archmage - decent damages but skills are good for shocking enemies and third skill can be used in combination with trap.
Demonologist - bad damages but good skills.
Shaman - a lot of totems to distract enemies so it's good.

Another unit combination is the Plant one:
- Ancient Trent - good damages + VERY tough
- Trent - decent damages + faster than Ancient Trent
- Faunt - bad damages, good skills though + resurrect plants.
- Spitting Thorn - Main Damages dealer in the group
- Royal Thorn - decent damges + very good skill

Retaliation Army:
- Demonologist - bad damges but good summoning and Resurrection skill
- Executor - Great damages, great skill, great abilities.
- Demon - see above
- Royal Griffin - Tough and good skill of summoning another unlimited retaliation ally.
- Griffin - Good damages and very tough with right protection.

Move-one-more army:
- Paladin
- Jarl
- Demon
- Executor
- Orge

Doom + Hel's Messenger does crazy damage, I've seen 65k so far. Ofcourse it depends on the stack size.

Later but whatever
 

Here I am, several years later trying the game and looking for a good combination. Guess I should have tried it long ago before loosing tons of troops but whatever...
I found the Rune mages + Demonologists + Jarls + Warrior Maidens to work very good (2 stacks of rune mages)
I usually cast armaggedon lvl. 2, spawn demons with Demo, then clone 2 stacks and summon as well, then just let the demons weaken the enemy and resurrect some troops with the maiden and 2 remaining clones of Demo before enemies get crushed by the summoned demons and clones.