Dark Depths by Stephan Martiniere
Marit Lage. An immortal horror from some distant and unknown realm, Marit Lage is a singularly-powerful plane-crossing titan. Vaguely resembling a kraken in her colossal form, her presence on Dominaria is long forgotten by most. After wreaking devastation on the plane, she was sealed in a glacier during the ice age, by powers or individuals lost to the passing of time. After the end of the ice age, Marit Lage’s fate has remained, unsettlingly, undetermined. She may still be imprisoned in ice in Dominaria’s frozen Northland (those few furtive scholars studying her speculate that the peninsula of Upper Videnth is the location of her icy prison), but Dominaria’s oceans are vast, and who can say what evils of time immemorial may bide their time in the depths…
Freeing Marit Lage. The ancient enchanted ice imprisoning Marit Lage is resilient to any attempts to break free from within, and requires immense amounts of magic to bring it close to suffering any damage at all. The ice surrounding Marit Lage has an AC of 22, 1000 hit points, and is immune to bludgeoning, slashing, piercing, cold, and psychic damage, and all damage from nonmagical attacks. In addition, the ice has a damage threshold of 30 – it has immunity to all damage unless it takes an amount of damage equal to or greater than 30, in which case it is damaged as normal. Any damage that fails to meet or exceed the damage threshold fails to affect the enchanted ice. When damaged, the ice slowly reforms, restoring itself by 100 hit points each week after suffering damage, until it has reach its hit point maximum of 1000 hit points.
The water beneath the ice is frigid, as described in chapter 5 of the Dungeon Master’s Guide. Within her prison, Marit Lage is restrained (and unable to use her Planar Peregrination ability).
Marit Lage as a Warlock Patron. For warlocks who hear the distant call of Marit Lage from beneath the ice, the Great Old One warlock patron best represents the powers Marit Lage can grant to her followers. A warlock of Marit Lage favours spells that deal cold or psychic damage, or are drawn from representing Marit Lage and the tenebrous waters of her prison, such as Evard’s Black Tentacles. Warlocks of Marit Lage gravitate towards the ocean, where the waters surrounding them grant the firmest connection to their eldritch patron. For a Pact of the Blade warlock, the summoned weapon would be engraved with motifs of black tentacles, and with glinting pieces of ice. For a Pact of the Chain warlock, an ice mephit could serve as an alternative option for a familiar.
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Dark Depths by Mathias Kollros