Here is the full list of all 6 Gladiator Guild Manager: Prologue achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Killed 200 enemy gladiators
Completed The Bridge arena and finished the Prologue version of the game.
Killed 25 enemy gladiators
Completed the first arena: The Graveyard
Killed 750 enemy gladiators
Finished The Game On Hard and Perma Death Mode