How does the Proficiency Without Level variant rule work for lvl -1 creatures?

Question

In Pathfinder 2 the Proficiency Without Level variant rule lists that:

Additionally, for creatures, hazards, magic items, and so on, reduce each statistic that would include a proficiency bonus by the level of the creature or other rules element. These statistics are typically modifiers and DCs for attacks, ACs, saving throws, Perception, skills, and spells.

This seems pretty straightforward for most cases: lvl 0 creatures don't change, lvl 1 get a -1 on all DCs and bonuses... But what happens for creatures with a negative level? (like, for example, a skunk?) Do they get a +1 on everything or do they stay the same?

The automatic calculator on Archives of Nethys considers that they should stay the same, but is this backed up by some rule? or is it a bug?

Answer 1

No Explicit RAW

Simply put, the rules on Proficiency Without Level (PWL) don't address this explicitly. So you have some options:

Most RAW: Subtract a Negative

In other words, RAW says to subtract their level from their stats. Their level is -1.

...reduce each statistic that would include a proficiency bonus by the level of the creature...

This should work okay, and level -1 creatures aren't relevant for very long.

My Preference

Level -1 creatures are really supposed to feel easy, even to the most basic of PC's. They're weaker than level 0 PCs! Plus, the rules for PWL have this interesting recommendation (for PCs, admittedly):

We recommend giving an untrained character a –2 proficiency modifier...

Level -1 are the basest of creatures. To make them still feel "base" to even the most basic of PCs, I'd actually subtract 1 more from their statistics. That nets a total of minus 2 from the baseline - minus 1 from their level pre-PWL and then an additional one. This lines up nicely with the untrained suggestion.

The Easy Way

Obviously, you could just use what AoN has. That should honestly work just fine, level -1 creatures are rarely a threat as it is.

Rebuild as Level 0

The lots of work but probably should work out okay option is to just rebuild them as level 0 creatures with PWL. This seems like a lot of work, but you shouldn't run into any real balance issues with them there. It has the nice advantage of making Level 0 PCs feel like the basest of creatures as well.