The Expanding Codex series fleshes out monsters from the Creature Codex, giving GMs ways to modify the existing monsters to surprise well-prepared players or to introduce monsters to a campaign.

Alternate Traits and Actions

The following changes allow GMs to alter moon drakes without modifying its challenge rating:

Shiftersense. The moon drake can sense the presence of shapeshifters within 30 feet.

The moon drake’s darkvision is reduced to 60 ft.

Mooncurse Slash (Recharges after a Short or Long Rest). Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: The target must succeed on a DC 15 Constitution saving throw or become cursed with lycanthropy (the moon drake chooses the type of lycanthrope). A creature that previously suffered from lycanthropy (even if it was cured) makes its saving throw with disadvantage. A lycanthrope has advantage on its saving throw. If a lycanthrope fails, it changes to the type chosen by the drake. This attack can’t affect a natural-born lycanthrope.

A GM who wishes to randomize the type of lycanthrope can do so as follows, on a roll of a d10: 1: werebear, 2: wereboar, 3: weretiger, 4–6: wererat, 7–10: werewolf.

The moon drake replaces the Moonlight Nip action with Mooncurse Slash.

New Magic Item and Spells

The following magic item and spells are inspired by a moon drake’s abilities:

Moon Drake Dagger

Weapon (dagger), rare

This dagger is fashioned from a moon drake’s fang. You gain a +1 bonus to attack and damage rolls made with this magic weapon.

You can use an action to imbue this weapon with additional magic for 1 minute or until an attack using this weapon hits a shapeshifter. That creature must succeed on a DC 15 Constitution saving throw or take 2d10 radiant damage. On a failed save, the shapeshifter instantly reverts to its true form and can’t assume a different form for 1d4 rounds. The dagger can’t be used this way again until the next sunset.

Alter Moon Phase

4th-level illusion
Casting Time: 1 action
Range: Self (1-mile radius)
Components: V, S, M (a pinch of moondust)
Duration: Concentration, up to 1 hour

You change the apparent moon phase for a 1-mile radius around you for the duration. If a creature within the affected area possesses abilities dependent on a particular moon phase, or change shape based on the moon phase, it must make a Wisdom saving throw to avoid being affected by this spell.

If you cast this spell at night, the altered moon phase can affect light. If you change the moon phase to full moon, light improves to dim light in the area. If you change the moon phase to anything other than full moon, light decreases to (or remains at) darkness. If you change the moon phase during the day, it has no appreciable effect on light.

Moonbeam Form

3rd-level transmutation
Casting Time: 1 reaction, which you take when you take damage or are restrained
Range: Self
Components: V
Duration: 1 round

You become an incorporeal beam of pure moonlight for the duration. While in this form, you have immunity to bludgeoning, piercing, and slashing damage from nonmagical attacks. While in this form, you can pass through openings at least 1 inch wide and through transparent objects. You also gain a flying speed of 90 feet for the duration.

Tidal Manipulation

2nd-level evocation
Casting Time: 1 action
Range: 1 mile
Components: V, S
Duration: Concentration, up to 1 hour

This spell creates a gravitational effect similar to the moon’s effect on tides. You can create your choice of low tide or high tides in an area up to a 1-mile radius from the point you designate. A low tide strands vessels and reduces flooding in the area, while a high tide might create flooding in an area. Vessels in a low tide are gently lowered to the seabed and take no damage.

You can use this spell to reduce the height of the wall created by the tsunami spell by 50 feet. This also reduces the damage dealt by the wall by 1d10.

Moon Drake Adventure Hooks

• The leader of a clan of werebears asks the PCs to stop a creature that has been transforming her clan members into ordinary humans. The PCs discover a pack of werewolves have tricked the moon drake into curing the werebears and weakening the clan, leaving the former werebears open to attack by the werewolves. If the PCs manage to negotiate with the drake, they might be able to turn the tables on the werewolves.
• If the PCs research cures for lycanthropy after one of the party is bitten by a wererat, they discover the location of a moon drake’s lair at the top of a tall mountain. Reaching the drake is difficult. Once the PCs find the drake, it is amenable to removing the curse from the afflicted PC. However, it may ask them to help eradicate the wererat nest or perform a similar task as repayment.