Aliens would need an oxidizer to metabolize as well, even if that oxidizer isn’t oxygen. If they want to actually efficiently get energy out of things, it’ll need to be a strong one. Even fermentation is a oxidation-reduction reaction that just doesn’t use oxygen.

Powerful oxidizers are dangerous stuff!

One I’ve learned about recently (and used) is potassium permanganate. One of its uses is for improving water quality in fish ponds. It oxidizes basically all organic matter. It can simultaneously knock out algae, bacteria, parasites, hormones, and other excess organic waste. And the pathogens it kills can’t build up resistance to it like they would an antibiotic or poison, so it can be used preventively without creating stronger bugs. You can’t really build resistance to BURNING outside video games.

But that also means that if you add too much, you can just as easily sterilize all life in a body of water, including fish and anything else you want to keep.

AND it means you need to be careful when handling it. If you burn your eyes or your lungs, it makes them stop working!

Sol 3 is a Class-14 Deathworld on what used to be a thirteen-point scale until they found it.

Not only is the planet very geothermally volatile with active volcanic systems AND feature violent and chaotic weather systems…

“Earth” is the deepest gravity well they’ve ever witnessed chemical rocketry successfully achieve orbit from.

The biosphere is teeming with pathogens, so much so that the sapient population’s own bodies rely on symbiotic microbial colonies in order to digest nutrients among other tasks.

And the macroscopic fauna are ALMOST as scary as the microscopic stuff: every biome packed with highly adapted predators.

At the top of this complex carnal carnival of carnivory, the “humans” who live there are unstoppable pursuit and persistence predators highly naturally gifted in ranged combat that historically used to just WALK their prey to death. The animals which ancient humans consumed could sprint to temporary safety, but humans will catch up, ALWAYS catch up, and the prey will still be tired when they have to sprint again. Eventually the fatigue outpaces them, and humans catch up for the last time. Just walk right up and bash them with a rock, they might not even have to throw it: dinner is ready!

Furthermore, it’s not just the highly volatile oxygen that all the animals there breathe… Sol 3’s atmosphere also even contains a constant background presence of radon. The biosphere is passively resistant to some levels of radiation. One of the cities was consumed in the fallout cloud of an exploding nuclear fission reactor(they STILL use water to cool their municipal fission reactors even now!), and although the humans fled, the animals that stayed there are FLOURISHING. Deformed and mutated, but thriving.

NOBODY SANE CHOOSES TO GO TO SOL 3.

We’re also reliant on water and are mostly made out of it. water is such a “universal solvent”, it’s quite OP. It dissolves so much, that we don’t even think about it

We’re death breathers, but also basically have acid blood like xenomorphs

This screenshot is an attack made by chemists with the intent to cause aneurysms on unsuspecting biologists.