Ok so I'm not 100% sure how -seed works, and I have heard that it "messes" with rng but not much about how it does so.

Today I experimented with -seed 121 and noticed that depending on what I had in my stash, inventory and belt, two different groups of monsters would spawn in jail lvl 1.

I did this maybe 20 times and it consistently worked when I compared having nothing in inventory at all and having 1 health potion in my belt. I could do the same thing by having or not having items in stash and inv.

Can someone maybe try to recreate this?

I can recreate that.

I shrine-leveled my naked amazon and started encountering a holy shock boss fetish when running low on potions (rejuv + 2 health potions + none in inventory) - with more potions I would encounter the 'usual' large group of flayers.

Timestamp to the holy shock boss ... and this for the usual large group of flayers

I farmed there for like 8 hours and only encountered the holy shock boss for a few runs until I figured out what caused him to appear instead of the group of monsters I was looking for.

The seed I was using is: -seed 604629284

Yeah in my testing with seed you needed to have an exact number of items on your character in total to replicate a specific monster spawn and/or drop from chests/breakable items near a WP.

48 Stash 40 Inventory 4/8/12/16 Belt 12 Equipped Items

Cube counts as one item slot too (meaning 37+12 for Inventory)

I think it comes to 121 maximum potential ways