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Auto-Scrolling Level: Averted in non-boss sections. Unusually for a Shoot 'em Up, levels don't scroll automatically. The only thing keeping you moving other than enemy fire is the time limit.
Awesome but Impractical: The blue power-up gives your submarine a missile that generates a horizontal ultrasonic vortex that sucks nearby enemies in, as well as damaging them. Unfortunately, it has a slow rate of fire, the missile itself isn't too strong, and for it to be effective it must not be blocked by enemies.
Bolivian Army Ending: The special ending you get if you beat the game with one credit may be an aftermath of this. It shows a whole load of enemy subs/ships wrecked up on the floor of the still-collapsing D.A.S HQ, followed by your submarine wreck in the middle of them. Most likely, your sub tried to confront all of them, and well, it didn't survive.
Boring but Practical: The red power-up just makes your ship shoot larger, more damaging versions of the standard weapon. Fortunately, it has the best rate of fire out of the three primary weapons.
Death Course: Two points in the game, in the sunken town as well as the enemy HQ. Your character has to pass over a series of rocket hatches that fire out large, long, indestructible missiles with rocket boosters near the top and bottom. Attacking the top rocket booster slows the rocket down, and attacking the bottom speeds it up. The problem lies in the fact that there is not enough space to squeeze in the area between two rocket hatches. You will have to use depth charges to slow down any rockets coming from below you, and regular torpedoes to speed up those in front of you, navigating across about 8-15 hatches or so of these at one go.
Difficulty By Console: The Playstation version takes you through all the levels in a slightly different order as compared to the arcade version, leaving the Deep Dark Sea as the fifth stage (instead of fourth), the Sunken Town as the fourth (instead of second), and the Ruins as the third (instead of fifth).
Do Well, but Not Perfect: If you managed to reach the final form of the Final Boss in one credit, you would get the special ending. It's not a happy one. Beating the game on more than one credit gave you the happy ending. Apparently, the boss has a "furious explosion" that destroys your sub should you get the bad ending.
Eye Scream: When low on health, Sougon's face explodes, revealing a organic interior with eyes dangling out of their sockets. It then gains an attack when it emits eyeballs which home in on the player.
Freeze Ray: Stage 1 has these attached to the sides of icebergs. While they cannot kill you, they immobilize your character in a block of ice for a short period of time, allowing other enemies to finish the job.
Improbable Weapon User: The anti-aircraft weapon, when used in the water, allows you to fire out balloons that float up to the surface and explode on contact. More useful than you'd think, as they can be rapid-fired into an enemy (as long as not many balloons are on screen), and the floating balloons will protect you from Death from Above.
Names to Run Away From Really Fast: While the English version calls D.A.S. "Dark Anarchy Society" (bad enough by itself), the original Japanese (which admittedly wouldn't seem like a viable organization name in English) is "Destroy and Satsujin". Fully translated: "Destroy and Massacre". Then there's the Deep Dark Sea boss J3. That's as in J-cubed, and the J seems to stand for "ja"—Japanese for "wicked".
Nintendo Hard: Your submarine, besides being a One-Hit-Point Wonder, has quite a large hitbox and is really slow. This makes dodging attacks a pain in the rear. Thankfully, most enemy projectiles can be destroyed, but the ones that cannot...
The first boss tries to ram into your character as one of its attacks.
The boss of the Channel also tries to do the same, hope you stayed low in the water!
Rewarding Vandalism: In the Channel stage, you are able to destroy the houses as well as skyscrapers. This not only nets you points, but the fallen wreckage also prevents the yellow robots from spawning underwater via tunnels.
Shoot the Bullet: Most of the enemy projectiles can be destroyed using your shots.
Shoot Out the Lock: In the Channel Stage, you will come across a bridge pillar blocking your way into the factory where the boss resides. You will have to destroy the bridge while a never-ending train carrying bombs (that drop on you) comes out of the factory.
If you manage to destroy Argock's grappling hooks, part of its body will detach, showing a mechanized fishbone interior.
Slippy-Slidey Ice World: The first stage takes place in Antarctica. Thankfully, you don't have to slip on the ice, and crashing into icebergs doesn't destroy you via Collision Damage. You do, however, have to fend off loads of submarines, turrets, helicopters, mines, and annoying Freeze Rays.
Spread Shot: The green powerup, of the exploding shot variety. You submarine shoots out a torpedo that explodes into armor-piercing shrapnel after a short distance. Unsurprisingly, it's the best weapon of the three.
Stationary Boss: The boss of The Channel Stage is a large robotic control unit for the factory, hanging from the ceiling. In its first phase, it cannot move; however, it has cannons on it that fire lasers which cause a laser-like spark to appear on the surface of the water.
Stuff Blowing Up: Almost all your enemies are mechanical (in fact, only three of them are organic) and explode when destroyed. Furthermore, as all your attacks and most enemy attacks are explosives of some sort, you'd definitely be sure to see a lot of explosions in this game.
The Dual Boss of the sunken town stage also exhibits this: once one of the two Trumpet Lilies is destroyed, the other will spam its missiles constantly instead of just trying to suck the player towards it.
The Stationary Boss of the Channel drops down into the water and floats about once it has taken enough damage. Manriki then tries to destroy the player via Collision Damage as well as periodically throwing out bombs.
Happens literally for the three-headed dragon snail — it gets redder when it is near death. Its attacks don't get any faster or deadlier, though.
Sougon's central face gets partially destroyed once you damage it enough, revealing its organic face. It then gains access to an attack where it emits eyeballs as homing projectiles.
Under the Sea: Naturally bound to happen as the player character was a submarine.
Underwater Boss Battle: Naturally, all of them, as your character is a freaking SUBMARINE!!! The only one that isn't a Type 1 is the boss in "The Channel" stage (it's a Type 4, where the boss hangs above the water).
Violation of Common Sense: You'd expect that beating the game on one credit will get you a Golden Ending that's even better than the Good Ending, but no. Doing a perfect run will net you one of the Downer Endings instead. If you want to get the good ending, you must use up more than one credit (read: see the Continue? screen at least once) before you tackle the Final Boss' final form.
Warm-Up Boss: The first boss, Argock, a giant mechanical fish. Its torpedo spam, while not easy to destroy, is very easy to avoid. Its next attack, where it tries to kill you with Combat Tentacles, is slightly harder to avoid — use your depth charges to push them away and avoid getting killed.