Here is the full list of all 21 Super Hydorah achievements.
Destroy Hydorah.
Unlock all achievements!
Destroy Hydorah and all his seeds.
Destroy Hydorah and all his seeds using no continues.
Find all hidden secrets in the game.
Find the chest of Grialia.
Score 500000 points or more.
Score 450000 points or more.
Score 400000 points or more.
Score 350000 points or more.
Find a pink elephant.
Score 300000 points or more.
Find a floating blue stone.
Score 200000 points or more.
Score 250000 points or more.
Find a giant green egg.
Score 150000 points or more.
Find a jumping flower.
Score 100000 points or more.
Score 50000 points or more.
Find an escaping astronaut.