A question on how the game deals with spawns

[Valase]

@Brian_Cahoon

Am I just getting unlucky in what I run into?

Yes.

@Brian_Cahoon

How does the game handle spawns and mutating mobs over time?

It depends heavily on your game settings, namely Monster evolution scaling factor and Spawn rate scaling factor.
This answer from an other topic explains it well:

Is monster evolution scaling bugged/backwards?

every zombie is assigned a ‘half-life’ value in days (i think standard zombies is 28). this value is the point at which half of the population of that type of zombie is expected to be evolved into the next type. some will do it earlier, some later, but that number is the mid-point or ‘half-life’ for that population to be upgraded. The evolution scaling factor is a multiplier for that half-life value. so at default 4.0 evolution the standard zombie has a half-life of 112 days (4x28)…again some WI…

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@Brian_Cahoon

Does making a new character change the spawns?

Since you’re playing in the same world, you can run into the same (already evolved) monsters or monsters with it’s timer getting close to evolving. If you go into newly generated terrain, I’m not sure, but I think it uses the (newly) generated evolution timer of your current character.

@Brian_Cahoon

What about [world] reset option?

To my understanding it wipes your world completely and just keeps the mod list. That should reset the timer for sure.

@Brian_Cahoon

Whats up with this dream stuff?

Dreams are mutation related. See the wiki pages on mutations and dreams (spoilers).
Or for short (taken from said wiki page): Once you are sufficiently mutated, you will begin receiving dreams, relating to how strongly mutated you are toward your highest category.