It's well known that the Heroic versions of Hearthstone's adventures pose a problem to many players, hardcore and casual alike. Heck, some of us never even completed Blackrock Mountain's wings on the highest difficulty. That said, we're here to provide you with some decklists, tips, tricks, and warn you about some things each of the bosses will throw your way. If you're interested in playing them without any outside knowledge, now would be the time to stop reading.
If you've missed our previous coverage of the Temple of Orsis, you can view our Normal guide here and our Class Challenge guide as well.

Temple of Orsis Heroic Guide

Zinaar Heroic

Along with an upgraded version of his hero power, Djinn’s Intuition, which also gives Zinaar a mana crystal
whenever he activates it, he's also done away with many of his weaker minions. Again, much of this encounter
depends on the cards you get as a result of the random wishes he gives you in the form of Wish for Companionship,
Wish for Glory, Wish for More Wishes, Wish for Valor, or Wish for Power. Basically we're looking to keep dealing
with his threats while building up a board of our own. Because he has more mana and is drawing more cards, even if we only
deal with his minions, we'll still win eventually.

Zinaar's Heroic Deck

Leper Gnome x2
Pit Snake x2
Rockbiter Weapon x2
Ironbeak Owl x2
Huge Toad x2
Whirling Zap-o-matic x2
Forgotten Torch x2
Mounted Raptor
Fireguard Destroyer x2
Desert Camel x2
Dunemaul Shaman
Anubisath Sentinel x2
Fire Elemental x2
Stormwind Champion x2

Mulligans

Keep: We want to keep anything that helps deal with early game pressure like Mirror Image, Mana Wyrm, and Frostbolt. The main challenge of this boss is to stay alive through the aggro.
Mulligan: Anything four mana or higher, they're simply too expensive and we'll be dead before we get to that point.

Sun Raider Phaerix Heroic

League of Explorers - Heroic Phaerix Silence Priest is the way to go with Heroic Phaerix. Because Rod of the Sun gets buffed to a 3/8 on his side of the field and is a useless 0/5 on yours, we're looking to kill it and then silence the deathrattle away. This is pretty much a gimmick deck where you need to have Shadow Word: Pain and then a form of Silence to even think about winning. After that point it's just a matter of staying alive and then winning with a Divine Spirit and Inner Fire combo.

Mulligans

Keep: Shadow Word: Pain and one form of Silence (either Silence or Ironbeak Owl). After that you just have to hope you have the right draws to stay alive.
Mulligan: If you don't have any of the cards you're aiming to keep, mulligan everything away. Without the Shadow Word: Pain, it is likely you'll lose right away.

Temple Escape Heroic

The Heroic Temple Escape is simply a harder version of the Normal encounter. You face the same choices, but the minions are much bigger. As a result, it's simply easier to do nothing than to actually worry about taking them down. And what deck is the best at doing that? None other than Freeze Mage. Even if you don't have all of the right cards, it's still your best bet if you have all the mass board freezes. We ran League of Explorers - Heroic Temple Escape Freeze Mage and managed to do it rather easily.

Mulligans

Keep: Mirror Image, Frostbolt, Frost Nova as these will help you deal with his early minions prior to the ceiling collapse. Once you get to that point it's usually much easier as you have more mana and can cast the higher cost spells like Blizzard.
Mulligan: This is another one of those hard mulligan decks. Without ways to stall until the ceiling collapse, you're going to lose.