I should just give you my DM's phone number. Dude's a fucking wizard at figuring out workarounds. High AC? Best of luck dealing with this paralyzing snake. Took the double your spell casting distance feat? Turns out the floor tiles are straight out of Zelda. You're a high dex rogue that can dodge all sorts of stuff? Here's 50 arrows fired out of an entire wall trap.

You can also fudge your rolls, but do it sparingly (I recommend only to save the players).

Surround the player with more enemies. Sure you won't really roll well enough to bypass their AC most of the time, but you'll hit them enough. When they win they just killed 8 kobolds so that's awesome but in the mean time they're gonna get wrecked.

We don't open chests by hand in our campaign, we attack them after checking for traps. Some stuff is just more likely to be a mimic.