Who's the Boss? Achievement in Immortals Fenyx Rising
Who's the Boss?25
Defeat the Mythical Monster bosses.
How to unlock Who's the Boss?There are four Mythical Monster bosses that need to be defeated for this achievement. Three of them can be fought at any time, but the fourth only appears after completing Athena's questline, at which point she'll gve you a side quest to defeat one of the Mythical Monsters.
The four Mythical Monsters are located in the four "corners" of the map: the northwesternmost island in the Grove of Kleos, the northeastermost island in The Forgelands, the southwestermost island in the Valley of Eternal Springs, and on top of the roof of the tallest building in the southeasternmost corner of Ajax's Fort in War's Den. Refer to THIS LINK to see screenshots of where exactly on the map each Monster is located. Defeat all four to unlock this achievement.