Every area has an area boss in this game.
With the Agon Wastes, there’s not a whole lot of other places you can go at that point in the game, so you more or less clear out the entire space before heading back to the Temple Grounds hub area. Not so with the other areas, especially the last. But the reward we get for clearing Agon is what enables us to really go and explore Dark Aether.
The Dark Missile Trooper is an interesting addition to this game. Not that there haven’t been several bosses along the way, but they’re all guarding unique items. This guy is just holding onto a single, normal Missile Expansion. He has a boss health bar and everything! Thankfully, unlike many of the other bosses, he’s quite weak. Area bosses have the longest fights by far, but as you can see here, there’s quite a range to the power of something declared a “boss”.