Here is the full list of all 20 Banana Step achievements.
Smashed success.
Smashed a Baby Monkey.
Smashed a Monkey.
Smashed Brothers.
Killed 30 Baby Monkeys.
Killed 20 Monkeys.
Killed 6 Brothers.
Killed a Gorilla.
Killed 10 Enemies in one game.
Killed 20 Enemies in one game.
Killed 30 Enemies in one game.
Achieved 10,000 score.
Achieved 15,000 score.
Achieved 20,000 score.
Achieved 30,000 score.
Killed 3 at the same time.
Be killed by monkeys.
Saw Gollira flying.
Died in 3 seconds
Unlocked All Achievement.