@ChrisPerkinsDnD … question about encounters: How do you keep low-level creatures a challenge for high-level players? …
— Lodewijk Boute (@Lodewijk_Boute) November 10, 2016
Low-CR creatures can still hit and wound high-level characters. I would add more of them or pair them with tougher creatures. #WOTCstaff https://t.co/jxUNPO3Prc
— (((Chris Perkins))) (@ChrisPerkinsDnD) November 10, 2016
I have experimented, and also found just adding number quickly becomes a slog. So decrease hp so they are essentially one shots. So you have 100 goblins but your fireball kills 20, and every swing is a kill….if used rarely can make your heros heroic.
You can also make them hit harder, so when they do hit, it is a bit scary.