GammaFinder Mutantiary part 1 (Hammerderm)

So we introduced some quick and easy rules for GammaFinder, a post-apocalypse campaign hack for Starfinder, introduced the concept of the Unburned World and its relics (Halidom), and then gave some Halidom game rules. We’ve done one pretty standard theme for the setting, and two really weird ones.

Since GammaFinder is remaining popular so far, I thought it was time for a Mutantiary (like a Bestiary, but for weird mutant threats). Of course, these can be used for any Starfinder-compatible setting.

We start, with the hammerderm.

PA hammerderm

HAMMERDERM          CR 7          [COMBATANT]
XP 2,400 each
N Large Magical Beast
Init +4 Senses darkvision 60 ft., low-light vision, blindsight (vibration, 60 feet); Perception +20
DEFENSE     HP 125
EAC 17; KAC 20
Fort +11; Ref +11; Will +6
Defensive Abilities bounce off
Speed 40 ft. (burrow 40 ft., swim 20 ft.)
Melee bite +15 (2d6+11 S)
Ranged ping +18 (2d6+7 So, deafen)
Space 10 feet; Reach 5 feet
Offensive Abilities ping
Str +5; Dex +4; Con +0; Int -4; Wis +2; Cha +0
Skills Athletics +14, Intimidate +14
Languages none
Bounce Off (Ex) When an adjacent character makes an attack against a hammerderm and misses, but misses by less than 5, the attack literally bounces off the creature’s hide and reflects back at the attacker. The hammerderm makes an attack roll with a +13 bonus and, if the attack hits, it does its base damage (not including Specialization, ability modifiers, or special abilities) to the attacker.
Ping (Ex) The vibratory sonar of a hammerderm can be focused into a massive damaging “ping”. This counts as a ranged sonic attack with a 30 feet range increment and the deafen critical hit effect. It can fire through a material the hammerderm is currently burrowing or swimming through, but not other materials in contact with it — a hammerderm can ping through the earth it is digging through, but not through a concrete slap or boulder sitting on the earth. A target hit by the ping must make a DC 15 fortitude save or be deafened for 1d4 hours.

Hammerderms are much feared alpha predators most common in areas with long stretches of uninterrupted soil or sand, such as planes, prairies, deserts, river deltas, and beaches. They appear to be some horrific blend of shark and rhino, though its unclear if they are actually a product of mixing the dna of these creatures of if the Unburned World process that created them simply followed the from of those natural animals.

Hammerderms have massively powerful passive sonar, able to sense virbations in soil, water, and even the air making them almost impossible to sneak up on. They also possess an offensive sonic “ping,” a deafening bolt of focused sonic energy projected from an organ known as the tintabulum that runs along the front ridge of their head. If a hammerderm is killed without using any bludgeoning or sonic damage, the tintabulum can be extracted and sold (making up treasure equivalent to the appropriate amount for the hammerderm’s CR).

Hammerderms travel alone or in mated pairs, except when the moon is visible in the evening sky before nighttime, when they gather in small herds of 7-12. Hammerderms give live birth to 2-4 “peens,” which emerge fully capable of fending for themselves. A typical hammerderm is 12-15 feet long and weights around 5,000 lbs.

This is Just The Beginning

If the Mutantiary proves popular, we can do so much more with it! If you are looking for more GammaFinder-appropriate mutant critters right now, you can check out the grizzly boar and rattle-cat, which were designed for Really Wild West, but also work great in GammaFinder!


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Thanks, everyone.

About Owen K.C. Stephens

Owen K.C. Stephens Owen Kirker Clifford Stephens is a full-time ttRPG Writer, designer, developer, publisher, and consultant. He's the publisher for Rogue Genius Games, and has served as the Starfinder Design Lead for Paizo Publishing, the Freeport and Pathfinder RPG developer for Green Ronin, a developer for Rite Publishing, and the Editor-in-Chief for Evil Genius Games. Owen has written game material for numerous other companies, including Wizards of the Coast, Kobold Press, White Wolf, Steve Jackson Games and Upper Deck. He also consults, freelances, and in the off season, sleeps. He has a Pateon which supports his online work. You can find it at

Posted on March 31, 2020, in Game Design, Starfinder Development and tagged , , , . Bookmark the permalink. Leave a comment.

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