The Costume Guy
This, sir or madam, is boss.
I'm visualizing . . . A turn-based aerial combat?
Mecha combat. Not turn-based. Sorta like Armored Core, but the player's mechs can't fly that well.
The boss itself is a massive floating fortress.
The boss fight seems somewhat turn based as the boss isn't constantly shooting at the player and fires in somewhat predictable patterns, with each pattern finishing with one of the big weapons firing. During the firing window of the main weapons, the boss becomes temporarily vulnerable (as an impenetrable shield created by black hole manipulation protects it normally). The time which the boss is vulnerable reduces each time it takes damage during the window... and if not defeated soon enough the window becomes zero. (Either by not destroying it during vulnerable phases or actual time passing). The third major weapon fired is always the charged particle cannon- and this is the only time the major weapon will not be fired directly at the player, and the boss cannot be defeated until at a very minimum of 5 phases.
The hero has allies on this battle, and they'll quickly be killed if they get caught by the boss's major weapons.
Taking a direct hit from one of the major weapons is instant death. (Except the VLS, which is just an unearthly swarm of missiles, which do serious damage, but unless you get hit by all of them, it's not going to kill you outright.) As there is NO EXPLOITABLE TERRAIN, the focus becomes one based on dodging full attacks while maximizing damage. With the major weapons, it's not really possible to avoid taking damage from the blasts, but as long as you're not stupid with dodging, it shouldn't kill you if you're good at damaging it and dodging the other weapons (light VLS fire, smaller Railguns, Gatling fire)