Here is the full list of all 21 Ogo achievements.
Complete the first level.
Complete a bonus level.
Complete 5 bonus levels.
Complete all levels.
Defeat the first boss.
Defeat the second boss.
Defeat the final boss.
Complete a non-bonus level without losing any lives.
Complete 5 non-bonus levels without losing a life.
Complete 10 non-bonus levels without losing a life.
Reach the high score of a level.
Reach 5 level high scores
Reach 10 level high scores
Reach 20 level high scores
Get a "100!" score 10 times in a row by defeating enemies.
Complete phase 1 of the first boss (level 11) within 50s.
Reach level 20 in Arcade Standard.
Reach level 50 in Arcade Endless.
Get a score of 10,000 in Arcade Time - Easy.
Get a score of 13,000 in Arcade Time - Normal.
Get a score of 25,000 in Arcade Time - Hard.