Lair actions in 5e: what changed in 2024, and how to use the map
In the 2014 rules a legendary monster in its lair took a lair action on initiative count 20, losing ties, and could not use the same one two rounds running. The 2024 Monster Manual dropped that separate turn: a legendary creature in its lair instead gets more uses of Legendary Resistance and Legendary Actions, and the lair's regional effects shape the area around it. Many DMs still write initiative 20 lair effects as a table choice, because a lair that acts on its own is the easiest way to make a boss fight about the room. Here is how to do that well.
· 5 min read · TerrainTale
How lair actions worked in 2014
The 2014 Monster Manual gave most legendary creatures a list of lair actions. On initiative count 20, losing initiative ties, the creature chose one and it happened: the ceiling dropped rocks, a wall of force rose, the water surged. It could not repeat the same effect on consecutive rounds. The action did not use the creature's own action or reaction; it was effectively the lair taking a turn.
That extra turn was the feature. A boss that acts once a round, plus three legendary actions, plus the room itself, keeps pace with a party of four or five and makes the battlefield change while the fight goes on.
What the 2024 Monster Manual does instead
In the 2024 Monster Manual, being in its lair increases a legendary creature's numbers rather than giving it a separate turn. A typical adult dragon has Legendary Resistance 3 per day, or 4 per day in its lair, and three Legendary Action uses, four in its lair. The lair section describes regional effects, the changes to land, weather and creatures around the lair, rather than a list of initiative 20 actions.
The result is a boss that is tougher at home but a room that no longer acts. If you are running a 2024 stat block as written, that is the rule. If you want the room to join in, the old initiative 20 structure is still a good tool; just be clear with yourself that it is an addition to the stat block, and scale the fight accordingly.
- 2014: a lair action on initiative 20, losing ties, no repeats.
- 2024: extra Legendary Resistance and Legendary Action uses in the lair.
- 2024: regional effects describe the area, not a turn.
- Initiative 20 effects in 2024 play are a table addition.
Write lair effects that use the map
The best lair effects need the terrain you built. A crypt with four sarcophagi gets an effect that opens one and releases a skeleton. A flooded cavern gets one that raises the water a foot, turning the lowest squares into Difficult Terrain. A throne room with a chandelier gets one that drops it. None of these are generic; each makes the players look at the map.
Keep it to three. Three effects, used in rotation, give variety without making the DM look up a list every round. Write each on one line with its area in squares or feet, its save and DC, and what it does to position. A good default for the DC is the creature's own save DC.
Move the party, do not just damage it
A lair effect that only deals damage is a second attack. One that moves people changes the fight. Push creatures 10 feet toward a pit, make a line of squares Difficult Terrain, block a doorway with rubble, douse the torches on one side of the room. Each of these gives the party a new problem to solve rather than a few hit points to heal.
Movement effects also make the monster's position matter. A dragon whose lair collapses the tunnel behind the party has cut off the retreat; a lich whose crypt seals the sarcophagus the rogue was hiding behind has taken away cover. The damage comes later, when the party is where the boss wants them.
Three sample effects for a crypt
For a crypt fight with a CR 12 undead lord, try these, one per round on initiative 20, no repeats. First, the dead stir: one sarcophagus opens and a skeleton steps out in an adjacent square. Second, grave-cold: a 20-foot-square area becomes Difficult Terrain until the next initiative 20. Third, the candles gutter: every flame in a 30-foot radius of a point goes out, and that area becomes Heavily Obscured to anyone without Darkvision.
The third one works especially well on a map with real light, because the players see the room go dark. In TerrainTale candles and torches cast shadows, so putting a group of them out changes what the table can see, not just what the DM says.