oh! good question, happy to help. Yes, I'm talking about lone weird big creatures. A giant flame spitting mantis, a dune-esque-worm-person-librarian, etc. For groups of lesser things or people I'm using bandits, but my group hasn't _fought_ these as much. Last night I used a Giant as a ~super mutant and it was actually a bit too much (they ran away though, wisely).
I'd use these as groups too, but my players wouldn't take them on (as long as I telegraph well). We've found that the PCs are real squishy, but they also keep spending their money on roleplay things instead of like, medicine or armor.
I also use swarm creatures (e.g. 100 hand sized aggressive moths...lots of bugs in my game, I guess) but I treat these as environmental hazards because unless you have a specific tool or weapon, fighting these doesn't make sense.