Disclaimer: I am not well-versed in the systems of Leviathan: The Tempest, so if you have any feedback in that regard, do share. This is not meant to be strictly balanced, per se. It's meant to give a similar feeling to the one you'd get from playing an actual Leviathan. This is mostly a creative exercise, so if you prefer to include the fansplat as is, go ahead.

The Wake (Persistent Condition)
When Starving or Ravenous, the Beast's Horror goes hunting throughout the local dreamscape to Inflict Nightmares [BTP Page 99], but the primal fear becomes a quasi-religious awe. Someone who loses all Willpower points to the Horror not only suffers Soul Shocked, but also suffers a Persistent version of Swooning. The Resolution mechanic for Swooning is turned into a source of Beats and Willpower.

Since the Soul Shocked Condition prevents Willpower restoration from Virtue and Vice, the victim is initially dependent on the Beast for immediate psychological support. If the victim performs a very risky, harmful or otherwise dubious action to try and gain the approval and favor of the Beast, she regains all Willpower and snaps out of Soul Shocked. However, the Persistent Swooning continues for [Horror's Power + Lair] days if the Horror was Starving, or indefinitely if the Horror was Ravenous.

In the latter case, the victim can only get rid of it by decisively confronting and rebelling against the Beast for a full scene regardless of the dangers involved. If this would involve harming the Beast in any way, they must spend 1 Willpower just to make an attempt, which does not add +3 to the associated roll. As a compensation, the victim gains Exceptional Success with 3 Successes on all rolls to track you down, discover information about you and carry out your commands, but only to the best of their understanding and increasingly fragile sanity.

Beat: The mortal draws unwanted attention toward you or puts bystanders in danger as a result of their mad devotion.

Causing The Condition: An abnormal Homecoming/Devouring, or establishing Family Ties with a monster who is related to the oceans, dreams or madness in some way.

Resolution: If the Beast has this Condition as a side-effect of their Homecoming/Devouring, he cannot permanently get rid of it on his own. By regaining all Willpower from Life trait or otherwise significantly reaffirming their remaining human side in a risky situation, the Condition goes away but returns at the start of the next Chapter. The ST decides how the Beast can achieve permanent Resolution, but it should be long-term work spanning a full Chronicle. Otherwise, this Condition is Resolved along with Family Ties, unless the Beast permanently decreases his maximum number of Chambers by one. This represents the Horror evolving at the cost of restricting its Astral territory.

Note: Heroes are immune to the effects of this Condition, but often kidnap or otherwise coerce those affected by it in order to blackmail and lure out Beasts.

Beasts with the Wake Condition receive the 2 dot version of the Colossal Horror Merit automatically (see below). If he already has that, upgrade it into the 4 dot version. However, he must have at least one Atavism or Lair Trait related to the ocean, dreams or madness in some way, even if they are not a Makara. Furthermore, whenever a Hero places an Anathema of the Bane type on you, it manifests as an increased vulnerability against electricity.

Colossal Horror (•• Or ••••)
Prerequisite: Beast
While inside the Lair or otherwise fused with the Horror, every dot of Horror Form you invest into Size gives +10 Size, up to five dots of investment. With the 4 dot version of this Merit, each dot invested into Horror Form gives +20 Size. Since your Corpus is equal to [Resistance Attribute + Trait Maximum Based On Lair], this humongous Size does not give extra Corpus.

Instead, it simply allows you to make Brawl or Weaponry attacks from a distance of up to [Size] meters due to the absolutely massive reach of your horrific limbs. However, moving your monstrous bulk to hit from such a distance with enough speed requires considerable effort. This is represented as the Beast making an All-Out Attack.

As a drawback, whenever a smaller opponent successfully Dodges this attack, you effectively suffer the Stunned Tilt. Any other effects must be bestowed by Atavisms or equivalent traits. At ST's discretion, other destructive Atavisms such as Titanic Blow and Dragonfire may also have their reach increased proportionally to your extra Size.

In the edge case that an Atavism or similar ability requires the Beast to sacrifice Defense (e.g. Monster From The Deep), he does not need to choose between applying Colossal Horror or said Atavism; he benefits from both.