So I setup Penumbra in “Dawn of the Overmind” to be a hex crawl though it didn’t work out as my PCs just flew around.  They saw the necrosphinx – a sphinx I described as having a mind-flayer’s head and clearly undead – but they never engaged it.  The necrosphinx itself is from 4e and the encounter build I stole from the LOST LABORATORY OF KWALISH.


Created long ago by the Vivamancer this undead sphinx has a mind flayer’s head instead of a male human head. It has long since escaped the control of the Vivmancer and now roams free. If its riddle is answered it will answer any 1 question truthfully about Penumbra.

The sphinx appears to have suffered ancient injuries to its head, which have healed and been replaced by mechanical components. Both the creature’s eyes are now glowing blue lenses, and its head is orbited by a number of spinning metallic devices. “entreat with me,” the sphinx says, “for the sake of knowledge. You do not appear entirely ignorant, and I look forward to adding whatever small knowledge you might possess to my collection.”

The Sphinx’s Riddle. Instead of asking a traditional riddle that the characters must solve, the enhanced sphinx demands that they ask a question that it cannot answer. This could be a riddle, a secret, a logical contradiction, or any other question — but the sphinx warns the characters that with all the knowledge it has collected throughout the years, it knows the answer to every question. If it fails to answer, the characters are allowed to cross to the island without paying the toll.

With its enhanced knowledge, the sphinx can correctly answer almost any question. To simulate this around the table, you might challenge the players to stump you as the DM with a riddle or trivia question. This might be something inherent to their characters’ own knowledge, or something completely outside the context of the game. If this is a question pertaining to the real world, you might tell the players in advance that you’ll make use of the Internet with a 30-second time limit to mimic the sphinx’s vast knowledge base. If this is a game-world question, you can instead let the sphinx attempt a DC 15 Intelligence check to answer the question, with advantage on the check (and look for further options in appendix B).

Each time the enhanced sphinx successfully answers a question, it demands that the characters pay the toll to cross: either one character’s Intelligence score permanently decreases by 1, or two characters each have another ability score of their choice permanently decrease by 1. This toll is magically extracted immediately, and manifests as another of the sphinx’s mechanical Ioun stone-like devices

Treasure. If the sphinx is defeated in combat, most of its mechanical Ioun stones shatter, reversing the effects of the sphinx’s tolls on all characters. Additionally, two Ioun stones survive and can be claimed. (If she is with the party, Mary Greymalkin covets these magical-mechanical devices, and turns against the characters if doing so helps her claim them). Choose these two unique stones from the new examples in appendix D.

Large undead, lawful evil
Armor Class 17 (natural armor)
Hit Points 199 (19d10 + 95)
Speed 40 ft., fly 60 ft.

22 (+6)
10 (+0)
20 (+5)
24 (+7)
18 (+4)
23 (+6)

Saving Throws Dex +6, Con +11, Int +10, Wis +10
Skills Arcana +9, Perception +10, Religion +15
Damage Immunities psychic; bludgeoning, piercing, and slashing from nonmagical attacks
Condition Immunities CharmedFrightened
Senses truesight 120 ft., passive Perception 20
Languages It can speak and understand all languages.
Challenge 17 (18,000 XP)

Second Wind (1/Day). As a bonus action, the sphinx can regain 50 hit points.

Regeneration. The sphinx regains 10 hit points at the start of its turn. If the sphinx takes fire damage, this trait doesn’t function at the start of the sphinx’s next turn. The sphinx dies only if it starts its turn with 0 hit points and doesn’t regenerate.

Despair.Any creature within 25 feet takes -2 penalty to attack rolls against the sphinx unless they are immune to the frightened condition.

Inscrutable. The sphinx is immune to any effect that would sense its emotions or read its thoughts, as well as any divination spell that it refuses. Wisdom (Insight) checks made to ascertain the sphinx’s intentions or sincerity have disadvantage.

Magic Weapons. The sphinx’s weapon attacks are magical.

Focus. As a bonus action, the sphinx can target a creature it can see within 30 feet of it and make that creature its focus. The target remains the sphinx’s focus for 1 minute, or until either the target or the sphinx drops to 0 hit points. When the sphinx makes an attack roll against its focus, it adds a d4 to its attack roll. If the giant attacks a different target while it has a focus, it subtracts a d4 from its attack roll.

Sphinx’s Challenge. The sphinx poses a question or riddle out of combat. If the challenged creatures refuse to answer or fail to answer correctly, the sphinx gains the following benefits until the end of the encounter: 1 extra claw attack as part of its death’s pounce action, an extra use of second wind, a +2 bonus to attack rolls, and a +2 bonus to all saving throws.

Death’s Pounce. The sphinx makes two claw attacks. If both hit, they each do an additional 5 necrotic damage.

Claw. Melee Weapon Attack: +12 to hit, reach 5 ft., one target.
Hit: 17 (2d10 + 6) slashing damage 21 (6d6) necrotic damage. If the target is a creature, it must succeed on a DC 16 Constitution saving throw or be cursed with mummy rot. The cursed target can’t regain hit points, and its hit point maximum decreases by 10 (3d6) for every 24 hours that elapse. If the curse reduces the target’s hit point maximum to 0, the target dies, and its body turns to dust. The curse lasts until removed by the remove curse spell or other magic.

Roar (3/Day). The sphinx emits a magical roar. Each time it roars before finishing a long rest, the roar is louder, and the effect is different, as detailed below. Each creature within 500 feet of the sphinx and able to hear the roar must make a saving throw.

  • First Roar. Each creature that fails a DC 18 Wisdom saving throw is frightened for 1 minute. A frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
  • Second Roar. Each creature that fails a DC 18 Wisdom saving throw is deafened and frightened for 1 minute. A frightened creature is paralyzed and can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
  • Third Roar. Each creature makes a DC 18 Constitution saving throw. On a failed save, a creature takes 44 (8d10) necrotic damage and is knocked prone. On a successful save, the creature takes half as much damage and isn’t knocked prone. In either case the target takes a -2 to attack rolls for the rest of the encounter.

Fierce Retort. As a reaction to taking damage the sphinx makes a claw attack against the triggering attacker (if within reach) and this attack does an additional 5 necrotic damage and the target becomes the focus of the sphinx. The sphinx also roars if it is able to.

The sphinx can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The sphinx regains spent legendary actions at the start of its turn.

  • Claw Attack.The sphinx makes one claw attack.
  • The sphinx magically teleports, along with any equipment it is wearing or carrying, up to 120 feet to an unoccupied space it can see.
  • Mind Blast (2 Actions).The sphinx psionically emits psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 15 Intelligence saving throw or take 21 (4d8 + 3) psychic damage and be stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Though it’s unlikely the PCs will find the sphinx’s lair it uses the standard lair actions of an androsphinx.