Warmaster Horus
Explorer
There are always bigger fish in the sea and as DM, you have access to them whenever you want.
+12 and +13+bless more often than not.
+4 prof
+5 dex
+2 archery style
+1 or +2 weapon.
The +10 damage is from the sharpshooter feat.
I was having this same problem until recently, and it all came down to finding a monster that was able to stack up against the PCs well. All my PCs are level 11, and there are 6 of them, so finding something that could be difficult to them at all was rather hard to do. I had thrown all manner of devils and demons, and even a beholder at them, and they slaughtered it all. Recently however, I found that by upping the tactics on the monsters I was using, I was able to separate the PCs and deal a lot more damage to them, nearly ending in a TPK with just a couple changes!
The biggest thing I found was to just keep hammering them. For instance, the last adventure they had was in a Frost Giant fortress. Frost Giants are only CR 8, so I thought they could handle a few of them. After they fought 2 in a watchtower, 2 in the guardroom, and another 4 in the main hall, I realized that they were blowing all of their abilities (spells, dailies, second winds, etc.) on these monsters just to keep them away. The last battle, one I thought they would be able to handle easily, turned out to be very frightening when an Ice Devil used its Wall of Ice to cut off the barbarian and the Paladin from the rest of the group, setting up an ambush from behind. It was the first time in YEARS my party actually felt afraid for their lives, and it's all because I never relented, never slowed down with the attacks.
Tl;dr
If you want to challenge your PCs, don't let them rest.
This is not as easy as simply not letting them rest. Clever groups, particularly groups with spell casters like mine (Wizard, Cleric, Bard) can dictate the pace of the resting, and it gets easier as they get more powerful.
Not every adventure can be a race against time, or railroad the players into not resting, such as the opening of HoTDQ. As a player I hated that opening, it was so contrived.
Not every adventure can be a race against time, or railroad the players into not resting, such as the opening of HoTDQ. As a player I hated that opening, it was so contrived.