Breedable legendaries (monster legends)

Arch Knight: Goldcore (breedable) + Esthirel (non-breedable)

Vadamagma: Skipples (breedable) + Duchess (breedable)

Nemestrinus: Rhynex (breedable) + Darknubis (breedable)

Rockantium: Musu (breedable) + Terracrank (breedable)

Thorder: Rabidex (breedable) + Tartarus (breedable)

Lord of the Atlantis: Razfeesh (breedable) + Drop Elemental (breedable)

Goldfield: Erpham (breedable) + Drop Elemental (breedable)

Darkzgul: Fayemelina (breedable) + Darknubis (breedable)

Nebotus: Obsidia (breedable) + Cthulu (non-breedable)

Worker Hulk: Pandalf (breedable) + Hyperion (non-breedable)

Ultrabot: Gold Ra (non-breedable) + Darknubis (breedable)

Laomu: Erpham (breedable) + Galante (non-breedable)

Unbreedable Monsters (Mostly Epic): -----------------------------------------------------------------------------------------------------------------------------------------------

Galante: through gems and special events

Hyperion: through gems, special events, and the adventure map

Esthriel: through gems, special events, and the adventure map

Gold Ra: through gems and special events

Cthulu: through gems and special events

Breedable Epics: ----------------------------------------------------------------------------------------------------------------------------------------------------

Goldcore: Rockilla + Flawless

Skipples: Scorchpeg + Boneticore

Tartarus: Duchess + Duchess

Duchess: Terracrank + Tartarus

Rhynex: Rawawr + Terrordactyl

Darknubis: Genie + Beefcake

Musu: Rockilla + Mersnake

Terracrank: Duchess + Tartarus

Rabidex: Electrex + Pandaken

Razfeesh: Mersnake + Mersnake

Drop Elemental: Gigargast + Mersnake

Erpham: Genie + Rawrar

Fayemelina: Tyrannoking + Raane

Pandalf: Genie + Molem

Ledovech: Razfeesh + Drop Elemental

Dragonian Beast: Thundenix + Tarzape

Note: The breeding recipes here aren't set in stone, you can get Epic monsters many other ways. As long as you have two monsters with at least one element of the monster you're trying to breed on each monster, there's a chance you can get that monster when you breed them together.

P.P.S: Look in cell shop for unobtainable monsters (hopefully cell week)