Polygon asked Keith Ammann, a designer whose book The Monsters Know What They’re Doing helped countless dungeon masters prep better encounters, to build a monster for a homebrew campaign. The result is a flying creature named Mooncrow.
The Request Behind the Design
The request came from a DM running a campaign set in a world where the sun and moon are locked in permanent eclipse. Light and warmth are scarce, and nature shifts dangerously. Intelligent species fight the wilderness constantly. Monsters tend to be mutations with unsettling traits.
The party is a mixed bag: a Path of the World Tree barbarian, a Battlemaster fighter, a custom bard focused on support, and a Way of Shadow monk. They favor close combat but lack spellcasting and ranged options.
The campaign recently crossed level 5, a notorious threshold in D&D’s 5th edition and its current 5.5 update. Classes grow stronger, and the Challenge Rating (CR) charts in the Dungeon Master’s Guide stop being reliable guides. That shift means DMs need to rely more heavily on their own judgment about what a reasonable encounter looks like, since the official guidance no longer applies in the same way.
Ammann’s Creative Process
Ammann started by choosing a creature type. He settled on Monstrosity, with Fey and Aberration as backups. The habitat became a plains biome, and the design leaned toward a flying creature with keen eyesight.
The joke was that “This isn’t a group that’s going to be subscribing to the New Yorker.” Ammann assumed most or all of these characters had dumped Intelligence as a stat, which makes illusions highly effective. The monster can cast Mirror Image and Phantasmal Force. It also has a high Armor Class to survive longer and can innately cast Bane, which subtracts 1d4 from attack rolls for everyone except the bard.
The visual direction came from the setting’s darkness. The creature is either inky black or semi-transparent dark gray, blending into the sky. Its name is Mooncrow.
Why a Flock Beat One Big Monster
Ammann considered whether the creature would be a solo monster or something that hunts in flocks. He chose the latter. Smaller creatures attacking individual players in groups of two or three works better than one big creature the party fights directly, because it forces the party to split their attention and coordinate against multiple threats at once.
A CR 1 or 2 fits level 5 characters. That’s 200 or 450 XP per monster. A Moderate Difficulty encounter for four level 5 PCs allows between 2,000 and 3,000 XP, which works out to five or six CR 2 creatures or between 10 and 15 CR 1 creatures. Given the DM’s experience running encounters with 15 monsters, Ammann chose CR 2.
The stat block consulted the Monster Statistics by Challenge Rating table from The Lazy DM’s Forge of Foes, written by Teos Abadía, Scott Fitzgerald Gray, and Mike Shea. A CR 2 monster normally has an AC of 13. Ammann bumped it to 15 with the “Ecliptic Veil” feature but reduced Hit Points to the CR 1 range to balance things out.
The Attacks and Spellcasting
The monster makes two attacks per round, dealing around 8 or 9 damage each. Part of that damage is Cold, as the creature absorbs the target’s heat to warm itself. Ammann drew on a trip to the Indiana Dunes to watch a solar eclipse and the chilly sensation when the sun was occluded.
Rage won’t reduce the Cold damage.
The spellcasting matches the CR 2 standard.
What This Means for Homebrewers
Ammann’s process is instructive for anyone building their own monsters. The key steps are:
- Understand the world and the party’s strengths and weaknesses. In this case, the DM knew the party lacked ranged options and spellcasting, which shaped the monster’s design.
- Choose a creature type and habitat that fit the setting. The Monstrosity type, the plains biome, and the flying, keen-eyed design all respond to the campaign’s permanent eclipse.
- Balance the monster’s defenses and weaknesses so it feels fair rather than frustrating. The AC boost and HP reduction together keep the monster within a reasonable difficulty range.
- Test the design against the party’s actual composition, not just abstract numbers. The DM’s experience running encounters with 15 monsters informed the decision to go with CR 2 rather than CR 1.
The result is a creature that respects the DM’s sanity while still delivering a memorable fight. Mooncrow is a flying, cold-absorbing illusionist with a name that fits its world.
The Bottom Line
Keith Ammann took a specific campaign’s needs and turned them into a usable monster. The design was created for Polygon, and it’s worth reading for anyone who wants to borrow ideas for their own campaigns.
The whole exercise shows how far professional design resources have come for homebrewers. Mooncrow is a calculated, named, tested addition to a campaign.
The eclipse world deserves a monster that feels native to it. Mooncrow does that. It’s a small victory for a DM who just wanted a fight that worked.
Key Facts Box
- Designer: Keith Ammann
- Previous work: The Monsters Know What They’re Doing, Making Enemies
- New work: Mooncrow, a CR 2 flying monster
- Publication: Created for Polygon
- Setting: A world locked in permanent solar eclipse
- Party level: Level 5, 5.5 edition
- XP budget: 2,000–3,000 for Moderate Difficulty
- Inspiration: Indiana Dunes solar eclipse trip
Source material: “I Had a D&D Designer Make the Perfect Monster to Torment My Group,” Polygon.
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