5 Ways to make D&D Combat more Challenging

The post below is written for 5th Edition D&D, but it can be adapted to other editions. Simply replace Disadvantage with -4 to Hit or possibly a percentile dice roll for an auto-miss chance. Difficult terrain slows movement to one half.

#1. Fog, Mist and Thick Smoke/Heat Mirages gives Disadvantage to Range attacks (including ranged spell attacks) for specific areas of the battle map.

"The smoke and heat mirage confuses your shot. You completely miss."

#2. Difficult Terrain slows down movement. Rocky terrain, small cliffs, lava pool and puddles, icy floors, flooded, swamp, extreme winds slowing movement, etc.

"You move slowly around the puddles of lava bubbling up from the cracks in the earth."

#3. Give the enemy higher ground AND cover. (And if the party flies, add a swarm of stirges, bats, other flying critters which attack any flying person.) The PCs need to climb or use a stairs / bridge to get to the upper level. Flying attracts too many stirges...

"As you fly upwards to get a better angle at the enemy a pair of opportunistic stirges swoop down to attack you from behind, aiming for your neck."

#4. Add a ballistae (or two) that is attached to the architecture. The enemies use it to shoot at anyone who is visible / out in the open. Give all attacks with ballistae advantage and they ignore / damage armour. This forces all of them to use stealth and cover. (Trying to take the ballistae with them should be extremely difficult and give them only 2 ballista bolts.)

"The ballista bolt rips right through your shield and armour. Your AC drops 2 points. You will need to get those repaired."

#5. Dangerous Obstacles / Traps DURING combat. Explosives Runes, falling rocks, pit traps, lava flows, falling trees that are on fire, the bridge collapses, smoke inhalation, rapids and rocks, etc.

"You charge forward towards the orcs when suddenly the ground beneath you collapses. Is it an earthquake? You land on sharpened stakes and realize you've fallen into a pit trap. The orcs laugh and cackle."