The green and orange on the tree trunk isn’t moss but, rather, an enormous collection of butterflies. The swarm of butterflies lifts from the rotten stump in unison and flies forward in a slow, fluttering mass. The air is heavy with the sweet smell of rot.
Death Butterfly Swarm CR 4
Creatures affected by the swarm’s distraction effect must also make a DC 16 Will save (Cha– based) or suffer from the effects of hold person. This paralysis only lasts as long as the victim is within the swarm.
Environment forests, mountains, temperate hills, and warm marshes
Organization solitary, pair, or cleansing (3–5 swarms)
Particularly vile creatures never seem to rest, often coming back as unliving abominations and ghastly spirits. Sometimes, though, these creatures do just cross over to whatever reward awaits them, leaving behind tainted corpses that pass the evil on to those that feast on the remains.
A death butterfly swarm results when a rare breed of carrion-eating butterflies, drawn to an incredible stench of decay, feed on the corpse of an evil creature. Individually, and prior to feeding on such a creature, the butterflies pose no threat, but the driving animus forces the butterflies to swarm and inflict misery on all who cross their path.
Naturally attracted to rotting material, the swarm’s new state allows it to inflict a fast-acting, necrotizing poison on its victims. Thus, it can feed immediately on carrion created with its poison. The oppressive evil infused in the butterflies bears down on those caught in the swarm’s wake, potentially paralyzing victims the swarm passes over. The swarm benefits from this effect, fluttering around unmoving victims and necrotizing more and more flesh while they cannot escape.
Undead creatures, to which the death butterfly swarm would obviously be drawn, are not immune to a death butterfly swarm’s poison. Just as the swarm rots away a living creature, it may also dissolve an undead creature’s animating force. Given the choice between an undead and living creature, the swarm always attacks the undead target. The swarm finds ghouls and ghasts to be particularly appealing.
Rumors persist of a death butterfly swarm that has fed on a particularly malevolent red dragon. The swarm possesses the breath weapon, special abilities, and SR of an ancient red dragon. Its poison has increased efficacy, dealing 1d4 Constitution damage over the course of 10 rounds and requiring 2 consecutive successful DC 20 Fortitude saving throws to cure. The swarm targets the dragon’s former enemies, but it also randomly attacks other creatures it encounters.