u/NobilisReed

I don't think alien self-replicating interstellar robotic probes are possible.

Here's my logic:

1. Any civilization that persists for an extreme length of time values its own perpetuation. If it does not value its own perpetuation, it will not persist for an extreme length of time.
2. Any civilization that develops self-replicating interstellar robotic probes (SRIRPs) must persist for an extreme length of time. An extremely long-term perspective is required for a civilization that will wait for thousands upon thousands of years for its probes to report back.
3. Any culture which builds a SRIRP will have previously built some kind of non-interstellar self-replicating robot, in order to develop the technology.
4. Mutations are unavoidable in a self-replicating system. No matter what template a machine is using, no matter what error-correcting systems exist, mutations remain possible, especially in the high-radiation environment of interstellar travel.
5. Any culture that does #3 must learn #4.
6. Any guardrails or controls built into a self-replicating machine can be eliminated or circumvented by mutations. This means that in the long term, guardrails and controls built into a self-replicating machine cannot be trusted to keep it from becoming a threat to the civilization that built it.
7. #6 is incompatible with #1. A civilization that values its own self-perpetuation and has the prescience to understand #6, will not build SRIRPs.

Any civilization which is capable of building SRIRPs will not have the will to build them; either they will be too short-sighted to see the benefit, or they will have enough of a long view to see that they are a threat to their continued existence.

THEREFORE: We cannot expect to find self-replicating robotic probes within the solar system.

EVIDENCE: Our solar system has not been destroyed by self-replicating robots. Therefore it is reasonable to assume that there are none in the galaxy.

EDITED to fix that weird font.

I've been thinking about how evasion and difficulty work, compared to D&D.

I really like how evasion and armor are (mostly) different things for PCs, but for adversaries I think they have to be combined for huge monsters. If you imagine swinging an axe at a monster the size of a dump truck, your chances of connecting are pretty good.

So when I'm describing a huge monster that's not supernaturally fast, I'm going to stress the places where it would be vulnerable, like eyes and mouth, belly, or in between its scales. When someone fails on an attack because it's below the difficulty, I'll describe it bouncing off the armor rather than missing it entirely.

That being said if I had an immense but also agile monster, like a serpentine dragon, I'll also allow it to dodge out of the way.

Our technique for beating Fader was as follows:

1> Breed up a hundred 1* asksvin
2> Build an earthen wall around the Fader arena
3> Release the asksvin into the arena
4> Summon Fader

The result:

1> We beat Fader without having to use our weapons once.
2> Due to lag, only one of us (the one hosting the session) actually saw Fader.
3> Only two of us saw Fader's health bar.
4> All I saw was unmoving asksvin disappearing

So as a means of cheesing Fader, it works.

But it's even less fun than cheesing Bonemass by standing on top of the skull.