Looking on this page of Tibia Wiki, https://tibia.fandom.com/wiki/Physical_Damage/Strong, you can sort by how strong they are against physical damage. For some reason there are multiple tables on the page so you will have to sort each one. Looking at this lists there are three creatures that are tied with 90% resistance.
The mushroom sniffer which you have listed, Modified Gnarlhound, and Spectre. I cannot confirm Spectres as I haven't unlocked them yet in my bestiary but looking at Modified Gnalhounds they are listed as 90% strong as well. Which is interesting because I just assumed they were immune to physical damage.
Reading the entry on tibia wiki it states "Despite not being really immune to physical damage, their extremely high armor makes it almost impossible to damage them using pure physical attacks."