17 Secret Video Game Bosses You Need To Beat Before You Die
2. Final Fantasy VII - Emerald Weapon
How you get there: Emerald Weapon becomes accessible as soon as Sephiroth pulls the dickish move of using the Black Materia to summon Meteor. When that awakens all of the Weapons, you'll be able to find Emerald Weapon cruising around at the bottom of the ocean. So yeah, that means you need the submarine to access the fight.
Why you need to beat them: The green, aquatic counterpart to Ruby Weapon is a much tougher fight the latter. Emerald Weapon not only has an extra 200,000 health over ruby (totalling at a cool 1,000,000), he also comes adorned with a foreboding timer placed above his head. You only have 20 minutes to down this monstrosity (unless you have a certain, ridiculously rare Underwater materia to nullify the timer), and leave his carcass at the bottom of the ocean.
If the 20 minute mark passes and you haven't already won, Emerald will instantly wipe your entire group and send you off to the game over screen to try again. Along with Ruby, Emerald forms one of the toughest hidden superboss battles of any Final Fantasy title, and the added pressure of the timer makes him an incredibly fun - if infuriating boss - to tackle.