- That One Achievement: "Complete Difficult Mode" on the 3DS version. All you need to do is complete the game on Difficult or Very Hard... without using any Smart Bombs and without getting shot down. Considering how hard the game is, especially when the Final Boss has so many phases as well as That One Attack.
- That One Attack: The Final Boss does this in his final phase, he charges up and fires out a nearly unavoidable wall of flaming death multiple times in rapid succession with a short cooldown between bursts. These walls of death cancel your shots and do collision damage with your plane. The only way around it is to hide behind asteroids or spam your Lightning Bombs (for temporary Mercy Invincibility). The 3DS remake makes this worse, where the boss now fires shots aimed at you while you're attempting to hide behind asteroids, in order to flush you out, and you have to move very carefully behind the asteroid to avoid damage.
- The previous attack is even worse, in which the boss fires fireballs and fire streams in sets of 3, is rather difficult to dodge effectively despite the order that the shots are fired from, and unlike the wall of flaming death, these aren't blocked by ANYTHING.
YMMV / Steel Empire