Here is the full list of all 44 GIGANTIC ARMY achievements.
Destroy 100 enemies with the UG-M Grenade Gun.
Unlock Hard Mode.
Beat the True Last Boss on Hard Mode.
Clear a stage on Hard Mode without taking damage.
Unlock Insane mode.
Play a stage in Practice Mode.
Equip at least 3 different combinations of main, sub and special weapons.
Achieve a final score of over 2,000,000 on Easy Mode.
Clear the game in Easy Mode.
Destroy 100 enemies with the SRI-U6 Riot Gun.
Clear a stage on Easy Mode without taking damage.
Destroy a boss using the MJ-88 Missile Pod.
Clear the game on Normal Mode.
Clear the game on Normal Mode with no continues.
Beat Stage 6 on any difficulty mode and with no continues.
Run into an electric grid in Stage 6.
Beat Stage 5 on any difficulty mode and with no continues.
Destroy 1,000 enemies.
Beat Stage 4 on any difficulty mode and with no continues.
Destroy 100 enemies with the ZAT-77 Assault Rifle.
Beat Stage 3 on any difficulty mode and with no continues.
Destroy an end of stage boss with no special weapons.
Destroy 500 enemies.
Block enemy attacks over 100 times with the Type S-95 SEC Shield.
Beat Stage 2 on any difficulty mode and with no continues.
Spend five seconds or more in the air (in one go).
Clear a stage on Normal Mode without taking damage.
Beat Stage 1 on any difficulty mode and with no continues.
Destroy 3 or more enemies with one shot from the SHAD-51 Cluster Bomb.
Destroy 100 enemies.
Stomp a land mine.
Clear a stage on Insane Mode without taking damage and with at least 140 seconds left on the timer.
Clear the game on Insane Mode.
Achieve a final score of over 4,500,000 on Easy Mode with no continues.
Achieve a final score of over 9,000,000 on Normal Mode with no continues.
Achieve a final score of over 13,500,000 on Hard Mode with no continues.
Achieve a final score of over 18,000,000 on Insane Mode with no continues.
Destroy 10 enemies with the SKB-BS Pile Bunker in mid-air.
Have your precious and expensive Type S-95 SEC Shield destroyed.
Destroy a boss using the GDW-76 Beam Cannon.
Destroy 10,000 enemies.
Destroy 100 enemies with the SKB-BS Pile Bunker.
Use your Vernier thrusters for more than 5 minutes in total.
Travel 10 km using the Dash Device.