Well, the Heroic Molten Core is definitely a step up in difficulty from the normal version, as expected.

It's not just a simple matter of increasing the minis' HP or other stats; some of the battle mechanics have been changed as well.

At the moment, I've cleared the first four bosses. Here's my walkthrough:

Boss 1: Lucifron (Heroic)

The Mind Controllers now have an aura around them. If you deploy an Unbound mini within this aura, it will die almost instantly.

So, the new strategy is:

  • Push your lane and establish control up to the towers and near the Mind Controllers.
  • Use an Unbound mini to bait the Mind Controllers' ability.
  • Once their ability is on cooldown, take them out with a spell or your other minis.

I used my high-level Arthas team for this, but I think other teams should work just as well.

Takeaways
  • Use unbound minis to bait the mind controllers

Boss 2: Magmadar (Heroic)

It seems the only change for this fight is that the enemies have higher levels and stats. I didn't notice any new mechanics.

Takeaways
  • Use Witch Doctor's Spirit Ward to protect your team
  • Huntress is effective here
  • You can beat this boss in many different ways.

To be honest, I'm not sure what the "best" team is for these bosses, as my higher-level teams pretty much steamrolled them.

Boss 3: Gehennas & Shazzrah (Heroic)

Spells are still disabled in this encounter, and the Flamewakers have significantly more HP (about 5 times as much), so you can't one-shot them with a S.A.F.E. Pilot anymore.

My friend used the Onu team, while I cleared it with a Sylvanas team.

Takeaways
  • Use a Quilboar to distract Gehennas (the red boss). Every time he stops at the left or right, he summons a Flamewaker. Using an Unbound mini to distract him will reduce the number of Flamewakers you have to deal with.
  • Use Sylvanas or a Meat Wagon to safely take down Shazzrah (the blue boss) from a distance.
  • Don't let the two bosses group up on the same side.

Boss 4: Garr (Heroic)

Heroic Garr is much harder than the normal version. His Earth Elementals now split into smaller ones when they die, which are difficult to clean up.

A Cenarius team focused on healing might be a good choice here:

  • Cenarius with Force of Nature
  • Bog Beast with Rampant Growth
  • Druid with Rejuvenation
  • Witch Doctor with Spirit Ward
Takeaways
  • Try to cast Execute on multiple enemies.
  • Don't deploy minis on earthquake areas.
  • AYou'll likely lose all of your minis after the first phase. Quickly rebuild your forces and push to the boss to secure the win.

Boss 5: Baron Geddon

WIP

Boss 6: Golemagg

WIP

Boss 7: Ragnaros

WIP