I thought some players may find this useful, I'll continue to update this list with new legendary heroes.
If you find a mistake let me know.
Crashed Hill (Difficulty V or above) x10 times:
Machinist - NEW
Frost Mage
Stormlord
Mystic
Light Bringer
Professional Killer
Valkyrie Showdown (Difficulty V or above) x10 times:
Succubus
Admiral
Cursed City (Difficulty V or above) x10 times:
Crossed Knight - NEW
Ninja Assassin
Ferryman
Wandering Spearman
Dwarf Warrior
Psychopath
Brute
Shallows Keeper
Emberstar
Rifleman
Drunken Master
Commander
Tidal Temple (Difficulty V or above) x4 times:
Psychic Sword
Wind Master
Depths Voice
Swordmaster
Cleric
Dwarf Arsenal (Difficulty V or above) x4 times:
Lightning Elemental
Imperial Executioner
Bear Warrior
Ice Mage
Savage One
Ice Spirit
Master Mage
Sniper
Outland Portal-Robot Fighter (Difficulty V or above) x4 times:
Poisoned One
Outland Portal-Raged Blood (Difficulty V or above) x4 times:
Death Knight
Outland Portal-Northern Dragon (Difficulty V or above) x4 times:
Mountain