Path of Blades

From Xanathar's Guide to Everything, page 118.

*Complex trap (level 1-4, dangerous threat)*

Hidden within a buried pyramid that marks the location of the Lost City of Cynidicea is the tomb of King Alexander and Queen Zenobia. The entrance to their tomb is a long hallway riddled with traps, accessible only by cunningly hidden secret doors. The hallway is 20 feet wide and 160 feet long. It is mostly clear. After 80 feet, the floor is broken and cracked, becoming difficult terrain until the 130-foot mark.

* **Trigger:** This trap activates as soon as a non-undead creature enters the hallway, and it remains active while any non-undead creature is within the hall.
* **Initiative:** The trap acts on initiative count 20 and initiative count 10.
* **Active Elements:** The Path of Blades includes a set of whirling blades along the first 80 feet of the trap, crushing pillars that slam down from the ceiling to the floor before rising back up to the ceiling in the next 50 feet, and a rune of fear in its final 30 feet.
	+ **Whirling Blades (Initiative 20):** The blades attack each creature in the first 80 feet of the hallway, with a +5 bonus to the attack roll and dealing 11 (2d10) slashing damage on a hit.
	+ **Crushing Pillars (Initiative 10):** Each creature in the 50-foot-long area beyond the first 80 feet of the hallway must make a DC 15 Dexterity saving throw. On a failed save, a creature takes 11 (2d10) bludgeoning damage and is knocked prone. On a successful save, the creature takes half as much damage and isn't knocked prone.
	+ **Rune of Fear (Initiative 10):** Each creature in the 30-foot-long area beyond the Crushing Pillars must make a DC 15 Wisdom saving throw. On a failed saving throw, the creature becomes frightened by the rune, and it must immediately use its reaction to move its speed in the direction of the pillars. The frightened creature can't move closer to the far end of the hallway until it uses its action to make a DC 15 Wisdom saving throw, which ends the frightened condition on itself on a success.
* **Dynamic Elements:** The blades and the rune become more dangerous the longer the trap remains active.
	+ **Blades Accelerate:** The blades move with increasing speed, slowing only when they hit a target. Each time the blades miss with an attack, their next attack becomes harder to avoid. After each miss, the blades' attack bonus increases by 2, and their damage increases by 3 (1d6). These benefits apply until the blades hit a target, after which the values return to normal.
	+ **Rune's Defense:** Tampering with the Rune of Fear increases the trap's power. Each successful check on an attempt to disable the rune increases the damage of the blades and the crushing pillars by 5 (1d10) and increases the rune's saving throw DC by 1.
* **Constant Elements:** The Whirling Blades and the Rune of Fear affect each creature that ends its turn in an area affected by these elements.
	+ **Whirling Blades:** Any creature that ends its turn in the blades' area is targeted by an attack: +5 attack bonus; 5 (1d10) slashing damage on a hit.
	+ **Rune of Fear:** Any creature that ends its turn within 30 feet of the far end of the corridor must make a saving throw against the Rune of Fear effect.
* **Countermeasures:** Each of the trap's active elements can be thwarted by particular countermeasures.
	+ **Whirling Blades:** Characters can smash the blades, damage their components, or discern how to avoid them. The blades are disabled if their attack bonus is reduced to -8. Ways to reduce it are described below.
		- *Intelligence (Investigation), DC 15.* As an action, a creature that can see the blades can attempt an Intelligence (Investigation) check. A successful check means that the character has learned how to anticipate the blades' movement, imposing disadvantage on the blades' attacks against the creature while it isn't incapacitated.
		- *Attack.* A creature in the area can ready an attack to strike at one of the blades as it goes by. The blade gains advantage on its attack against the creature. The creature then attacks. Each blade has AC 15 and 15 hit points. Destroying a blade reduces the Whirling Blades attack bonus by 2.
		- *Dexterity check using thieves' tools, DC 15.* Creatures can use thieves' tools in the area attacked by the blades to foil their mechanism. A successful check reduces the Whirling Blades attack bonus by 2.
	+ **Crushing Pillars:** The pillars are not susceptible to countermeasures.
	+ **Rune of Fear:** The rune can be disabled with three successful DC 15 Intelligence (Arcana) checks. Each check requires an action. A creature must be at the end of the hallway to attempt the check, and only one creature can work on this task at once. Once a creature attempts a check for this purpose, no other character can do so until the end of that creature's next turn. Alternatively, the rune can be disabled with three successful castings of Dispel Magic (DC 13) targeting the rune.