Here is the full list of all 27 Lost Bros achievements.
You defeated the boss of 10,000 BC.
You defeated the boss of 220 BC.
You defeated the boss of 1692 AD.
You defeated the boss of 2237 AD.
You answered three Sphinx questions correctly.
You defeated the Minotaur, Medusa, and the Hydra in 735 BC.
You spent your hard earned cash on the orb from 1864 AD.
You purchased the sunglasses and cutoff shorts.
You defeated the boss of 1968 AD.
You unlocked the field jacket for gunman.
You defeated the boss of 1742 AD.
You dug up fifteen things.
You collected all 9 orbs!
You unlocked all 9 upgrades!
You beat Lost Bros!
You got the worst Lost Bros ending.
You got the mid Lost Bros ending. (Beat the game in under 10 hours)
You got the best ending! Awesome job! (Beat the game with under 200 deaths)
Everyone survived the final sequence.
You've died 1000 times.
You beat the game on hard.
Wow..you beat impossible...here's a wheat muffin..
Kill the owl in the swamp.
Use the jukebox.
You collected all 3 masks.
You died for your first time.