Swarm of Stonebreaker Spiders

homebrew , monster

Large swarm of tiny beasts, unaligned

Armor Class 10 (Natural Armor)

Hit Points 72 (16d8 + 54)

Speed 25ft., climb 25 ft., burrow 10ft.

-4
3
+4
18
+1
13
-5
1
-2
7
-5
1

Damange Resistances Piercing, Slashing

Condition Immunities Charmed, Grappled, Paralyzed, Petrified, Prone, Restrained

Languages --

Swarm The swarm can occupy another creature’s space and vice versa, and the swarm can move through any opening large enough for a Tiny insect. The swarm can’t regain hit points or gain temporary hit points.

Frenzied Stone Eaters If a petrified creature is within range, the swarm will use all its movement to enter its space and attack with a Bite. If multiple petrified creatures are within range, the swarm will move to the closest. The swarm will ignore all threats while moving, including dangerous terrain, area effect spells, and opportunity attacks.

Stone Breakers The swarm’s Bite attack does double-damage against stone, including petrified creatures.

Stone Burrowers The swarm can use 5ft of its movement to burrow into a volume of stone at least 5ft square, or 2ft square if the swarm has half of its hit points or fewer. It has total cover while burrowed inside stone.

Hard Target While occupying an non-petrified creature’s space, the swarm has 3/4 cover (+5 bonus to AC) if the creature is fully clothed, or half-cover (+2 bonus to AC) otherwise.

Spider Climb The swarm can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Web Sense While in contact with a web, the swarm knows the exact location of any other creature in contact with the same web.

Web Walker The swarm ignores movement restrictions caused by webbing.

Hydrophobic Stonebreaker spiders will not willingly enter any wet space and can be forced to flee by spraying them with water or similar liquid.

Actions

Bite Melee Weapon Attack +6 to hit, reach 0 ft., one target in the swarm’s space. Hit: 10 (4d4) piercing damage, or 5 (2d4) piercing damage if the swarm has half of its hit points or fewer. On a hit, the target must succeed on a DC 13 Constitution saving throw or become petrified.

Reactions

Recoil When the swarm takes damage, it must use its reaction to leave the space it is currently in and burrow into stone 10ft or fewer away. If stone is not close enough for burrowing, the swarm moves to the nearest space, moving away from its attacker. If there is no unoccupied space and no stone available, the swarm does not disperse.

The stonebreaker is a small spider, not more than 2cm in length at adulthood, with grey-brown mottled carapace and two sets of mandibles. The stonebreaker lives in colonies burrowed deep inside rock, stone and old masonry. Colonies are recognizable by extensive criss-crossing spider webs that protrude from porous holes in the stone, which alert the spiders to prey entering the area.

When hunting stonebreakers attack as a single unit, dozens of spiders swarming the prey and covering it in dozens of tiny bites which can cause petrification. When their prey turns to stone, the spiders will enter a frenzy and begin rapidly consuming the hapless creature, first breaking it into large chunks and then into ever-smaller pieces to be carried back into the colony.

When attacked, the swarm instinctively recoils and retreats back into its lair when possible, but will re-emerge seconds later so long as prey is available.