Building a Boss Monster: Crypsos the Cruel

This article delves deeper into the point crawl we built last week using material from the supplement “Blackwater Citadel.” Specifically, we are building a boss monster for the final confrontation in the Throne Room of the Drowned King. This boss monster is Crypsos the Cruel, an ancient kraken from the depths of the ocean.

Start with the fiction: Who is Crypsos the Cruel?

When we think about boss monsters, or any monster we want to use in our game, we always start with the fiction. What is this monster? What does it want? How do we want the characters to see this monster?

For Crypsos the Cruel this fiction comes down to three major points:

Crypsos is an ancient kraken. A tentacled monstrosity from the bottom of the ocean.
Crypsos has crawled out of the depths and become the new king of Blackwater Citadel. He now commands many of the abominations within the fortress. He rules through fear and horror.
Crypsos feeds on the extraplanar energy of pure evil within the fortress. Specifically, he uses necrotic power surging through the Throne of the Drowned King to empower himself.

Customize an existing statblock: The kraken in Blackwater Citadel

Instead of building a new monster from scratch, which can be a painfully long process, we can customize an existing statblock to build our boss monster. We already have a kraken statblock in 5th edition, so let’s use it and bring it to life with the fiction of Crypsos the Cruel we outlined above.

Extraplanar energy. The throne gives Crypsos access to the energy of pure evil that flows through Blackwater Citadel. We can represent this mechanically by adding 10 (3d6) necrotic damage to each of the kraken’s attacks. In our descriptions we let players see how black energy seeps from the throne into Crypsos’s tentacles. If the players are smart, they might be able to remove Crypsos from the throne, or even destroy the throne. Both solutions would likely remove the added necrotic damage.

Fish out of water. Crypsos is no longer in the natural habitat of a kraken. He has made Blackwater Citadel his new lair. To represent this adaptation, we can let Crypsos use the lair actions of the kraken within the throne room. Even those lair actions that usually require water, work through the air as long as Crypsos remains the king of Blackwater Citadel.

For the king! Crypsos rules over Blackwater Citadel with an iron fist (an iron tentacle?). His minions obey him unquestioningly. We can represent this in the statblock by replacing the Ink Cloud legendary action with a new legendary action called “For the king!” By using this legendary action, Crypsos lets all of his allies within the throne room move up to their speed and make one attack. Depending on the number of minions this might be more or less effective, so we can adjust the number of legendary actions it requires accordingly.

Combat outs: Ending the boss fight early

In any combat encounter we can think about potential “outs” for the player characters. How could they end the encounter without reducing Crypsos to zero hit points? There are three obvious combat outs with others arising spontaneously during play:

Crypsos wants to live. Crypsos is no mindless creature. If he is reduced to below 40% of his maximum hit points he will crawl out the throne room and try to escape into the depths of the ocean. The characters might give chase, and we might have a cool underwater chase on our hands.
If someone else manages to seat themselves on the throne during the encounter, they can attempt to temporarily become the king of Blackwater Citadel. A high enough Charisma check might be enough to prove their worth to the throne. Alternatively, a character might be required to commit some evil act before they can become king. If the character is successful, the throne lets them punish Crypsos. A character can cast banishment through the throne, targeting Crypsos.
In the point crawl, the characters’ goal is to retrieve the fey war chest hidden within the throne room. If they manage to find and recover the hidden war chest while staying alive against Crypsos, they can run with the chest. In this case, it is probably best to drop initiative, and fall back to Ability checks and descriptions of the escape.

The king of Blackwater Citadel: Customizing a boss monster

As we have seen, to build a boss monster, we don’t have to be professional game designers. It can be as simple as grabbing an existing statblock and customizing it to make it fit the narrative we have in mind. The most important step in this process is thinking about the fiction of the monster. The story informs the mechanics. The more we have the fiction front and center in our minds while preparing and running the game, the more we will be able to create a unique encounter.

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