I took the "Dark Champion" achievement description completely wrong lol

[failure face]

It turns out that I can't get it this way, I was supposed to beat the final boss in Dark Matter Mode... which is so much simpler than what I did:
0. Don't use Dark Matter mode. Play on normal mode.
1. Start the Extinction mission as an asteroid, the one where you have to wipe out the Space Dinosaur's home star system with a dark matter asteroid. Mission progress may need to be cleared first, since this mission is crucial to victory.
2. Go to the forward command post, where there is a dark matter asteroid. You cannot "absorb" this particular asteroid... as an asteroid.
3. Absorb nearby asteroids until you become a small planet. Make sure to keep the dark matter asteroid on screen at all times; I'm not sure how far away the "unloading boundary" is but since it's no longer a mission objective it won't be kept around long.
4. As a small planet, get the dark matter asteroid to orbit you. Press Ctrl to absorb all asteroids. You now have one Dark Matter and therefore appear to qualify as a Dark Matter planet. Play the rest of the game normally from here on out.
5. Once you're a Large Dark Matter Star, save to one of your files. Respawn as an asteroid and complete the Extinction mission chain so that the final boss mission will (re)appear.
6. Go back to your Large Dark Matter Star. If you're like me and your prior strategy was "ram it with your stars until it dies", you'll have to form a new strategy to win this battle. Pick up some planets, don't absorb them, and challenge the final boss. Essentially your strategy here is to circle around the boss stars and smash them with planets, including the ones they throw at you.
If I ever get a longer-term screen recording working, I'll make a video of this. It's really entertaining, at least for me, because I can rest assured that if I'm suddenly obliterated out of nowhere, my aggressor will be consumed by the resulting black hole. Revenge!

[RattleM8]

how did you ever summon up enough effort