Two of the
magic antagonists I had in mind was
1) someone who has just been using magic to copy and hive-mind themselves, with their magical body-production making them a threat to other people who now ALSO need to use the same body-duplicating magic to keep up. Naturally this spirals out of control until magic is turned off so that these hive-minds die.
2) Healing-Spell-gone-wrong that just turns-off death in an increasingly large area. Bacteria, cancer cells, etc just don't die anymore and start drawing on magic for sustenance. This pink-goo just starts blobing over the area and expanding through the
node system to other planets.
3) ALIYUMS: I 100% imagine the ancient Aoi-Si have run into the Aliyums at some point. The Aoi-Si have magic and FTL and all that other stuff while the Aliyums ONLY have technology that is sorta plausably near-future just really well developed. I imagine the Aoi-Si easily defeated the Aliyums planetside for hundreds of years until their planets just started exploding with no warning. The Aliyums response to these attacks with no real way to attack back due to the timescale involved was to build a giant mirror array around a star to fling RKVs at Aoi-Si worlds at near lightspeed.... of course it would take hundreds, thousands, or tens of thousands of years for the attack to arrive.
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Further, I kinda like the idea of it being an
Echoni inside of a Grawla-Iconman to be the one to re-enable the system by kinda-accident, starting with forming a basic bridge between a few worlds starting on Hawking and then having the system start to gradually power back up across the Galaxy.