ASO II: Last Guardian (also known as Alpha Mission II) is a vertically scrolling shooter released by SNK in 1991 for the Neo Geo arcade and home systems. It was later released for the Neo Geo CD in 1994.
The player controls a fighter spacecraft (Armored Scrum Object) and can shoot enemies in the air, bomb enemies on the ground, collect power-ups, and defeat bosses to advance levels.
Ten years after the events of Alpha Mission, the Seven Star Alliance, now lead by the gigantic transforming android Fulvar, has resumed its war against Earth. In response, the high-performance space fighters SYD-RX and SYD-FX have been dispatched from the space carrier Dolphin to curb the Alliance's assault.
The game has only 2 or 3 buttons used depending on the selected shuttle mode. Pull the joystick to maneuver the shuttle. The first shuttle mode enables you to fire missiles and laser shots simultaneously with Button A, but in the alternate mode press Button A for laser shot and Button B for missile shot. Laser shots are used for air-to-air attacks and Missiles are used for air-to-ground attacks. When a drone is shot, power ups can be collected: S for Speed, L for Laser shots, M for Missile shots and G for credits. Credits are useful for purchasing weapons in between stages. The power ups are changed by shooting them. When Laser shots and Missiles are maxed, they are more widespread and combined in power. There Hidden items can do certain things like an R item can put the shuttle in Reverse for a certain distance. The shuttle is destroyed by the one shot or by running into an enemy unit or hazard. Unless the player gets far enough, the missiles and laser shots will be lost to minimum power.
Press Button C (on the first mode)/Button B (on the alternate mode) to bring up the weapons selection provided you have weapons available, select the weapon with Button A. To cancel the weapons selection press the button used to bring it up. Different weapons serve different purposes.
Laser - Replaces ship's laser fire with two large laser blasters. Can be charged to fire a widespread laser beam attack that covers nearly 80% of the screen.
Homing - Fires 6 extra air-to-ground homing missiles on command. Ideal when used near the center of the screen.
Side - Adds on two additional laser drones to the sides of the ship that automatically rotate and point at targets. Can be used both offensively and defensively.
Bubble - Replaces the ship's laser fire with a bubble gun. Only two bubbles can occupy the screen at any given time. When the bubbles reach an aerial target, it will explode and either completely swallow up the enemy or cause large amounts of residual damage (the bubble explosion will not move from where it originally exploded). This is one of the few armors capable of destroying the falling glass panels.
Shotgun - Fires two air-to-ground flame columns in a straight line forward on command.
Shield - Creates a force field around the armor. Has the highest defense rating of all the armors, but forces the ship to occupy more space on screen. Though normally meant for defense, it can be used for offense on command by replacing the shield with 6 energy balls that can be charged and released. Note that the shield is down during this time, so the armor's defense is lower when using this attack. When released, the energy balls fire out in a spiral fashion to take out aerial targets.
Nuclear - Fires a single missile on command that causes a large explosion that can take out both aerial and grounded enemies.
Black Hole - Fires a black hole on command. The black hole swallows up all small-medium aerial targets and destroys nearby, small grounded targets. Only one black hole can be active at any given time. Regular missiles cannot be fired while a black hole is active, but lasers are unaffected. All enemy attacks are neutralized while the black hole is active.
Fire - Replaces the ship's regular laser and missile with a powerful flamethrower. This flamethrower can attack both aerial and ground targets and possesses an extremely high damage output. The fire can also destroy energy shots.
Phoenix - Can charge up power to create a defensive phoenix shaped aura around the ship, rendering the ship invincible. When released, the phoenix aura flies forward to cause large amounts of damage to both aerial and ground targets. Energy is continuously (and rapidly) consumed while the aura armor remains around the ship.
Thunder - Arguably the most powerful armor in the game. On command, flies to the center of the screen to unleash a screen-filling lightning attack. Eliminates all targets and energy bullets on screen or otherwise causes large amounts of damage to enemies not destroyed. Also uses the most energy of all the armors.
The weapons have a limited power indicated on an energy meter on the left of the screen. Using the weapons or getting the ship damaged lowers the energy. The energy can be recharged by E power ups.
There are seven stages in the game. The player has to fight through them avoiding hazards in addition. Mid-bosses very occasionally appear in the game. When the player meets an mid-boss or end stage boss, the player must destroy weak points and various parts of the boss to destroy it.