A crystalline tick hops off the neck of the dead wizard and flies behind a bookshelf, where it changes into a harmless-looking silver ring bearing an arcane symbol.

A Bane of the Arcane. The arcamag is a creature that survives by feeding on the magical force within creatures, especially humanoid spellcasters. An arcamag looks like a tick comprised of jagged, clear-crystalline fragments. Barbed hooks springing from its mandibles allow it to attach to a host. Symbiote or Parasite? The arcamag waits until a spellcaster takes possession of it, stowing it in a backpack or belt pouch. At that point, it changes into its natural form and works its way beneath clothing to a covered piece of flesh: the small of the back or the inner thigh are prime locations. Once there, the arcamag attaches to the caster. In the short term, a caster might benefit from acting as a host, but, in the long term, the consequences can be devastating and potentially fatal.

Use in Battle. Arcamags are occasionally used by war wizards in battle, hoping to bolster the magical might of their troops. Sometimes this works, but, more often than not, inexperienced wizards are left dead on the battlefield.

Arcamag

Tiny monstrosity (shapechanger), neutral
Armor Class 13 (natural armor)
Hit Points 22 (5d4 + 10)
Speed 10 ft., fly 30 ft. (hover)

STR	DEX	CON	INT	WIS	CHA
7 (-2)	10 (+0)	15 (+2)	5 (-3)	12 (+1)	18 (+4)

Skills Stealth +4
Senses darkvision 60 ft., passive Perception 11
Languages understands Common but can’t speak
Challenge 2 (450 XP)

Camouflage. While attached to a host, the arcamag has advantage on Dexterity (Stealth) checks.

Shapechanger. The arcamag can use its action to polymorph into a small object, such as a ring, wand, orb, rod, or scroll. Its statistics are the same in each form. Any equipment it is wearing or carrying isn’t transformed. It reverts to its true form if it dies. False Appearance (Object Form Only). While motionless, the arcamag is indistinguishable from an ordinary object.

Actions

Attach. Melee Weapon Attack: +2 to hit, reach 5 ft., one creature that can cast spells. Hit: The arcamag attaches to the target. While attached, the arcamag doesn’t attack. Instead, it causes a handful of changes in its spellcaster host (see Changes to the Host sidebar). The arcamag can detach itself by spending 5 feet of its movement. A creature other than the host can use its action to detach the arcamag by succeeding on a DC 15 Strength check. The host can use its action to detach the arcamag only after the host has expended all of its spell slots for the day, including the extra cantrips and spell slots gained from having the arcamag attached. Doing so doesn’t require a Strength check. When the arcamag detaches itself or is detached from a host, the host takes 2 (1d4) psychic damage per spellcaster level.

Teleport (1/Day). The arcamag magically teleports up to 60 feet to an unoccupied space. If it is attached to a host when it uses this action, it automatically detaches.