I was wondering at what level disparity could I use a brute (or any other non-solo mob type) as a solo challenge for my players? Is there a rule of thumb to follow?
The example I had specifically in mind is a level 9 brute (shambling mound) vs. 3 PCs with 2 companions (level 4 party). Party consists of a fighter, cleric, wizard and the two companions make up the rogue and damage dealer side of the striker role.
Thanks in advance.