Here is the full list of all 8 Gun Monkeys achievements. It takes around 5-6 hours to unlock all of the achievements on Windows.
Win 10 games in a row.
Win a game with the Masochist perk.
Win a game without dying.
Play a Local Game against a real-life friend.
Win a Jetpack Match.
Get a full-length tail.
Break the tutorial.
Beat an opponent who has the Monkey Fever virus.