Jaculis looked like snakes with mauve to dark purple scales and an arrow-shaped head topped with sharp, forward-pointing horns. Some members of this species displayed heads that were more broad and flat, with razor-edged horns projecting as a ridge on either side.
These creatures were not innately aggressive or hostile towards others, though they were very territorial and easily excitable.
Jaculis were capable of camouflaging themselves, comparable to the famed ability of a chameleon, changing the color of their skin to match their surroundings. They were also known to be talented climbers and swimmers. Some described them as being capable of launching themselves with a force and accuracy comparable to that of javelins.
Jaculis lured in their prey with animal trance, then attacked with its sharp horns and its ability to constrict. If a foe proved too troublesome, jaculis jumped from tree to tree to escape, then swung around and pursued the prey for a better opportunity.
Jaculis could live in nearly any environment, though being serpents they had a preference for warm climates. Furthermore, being arboreal creatures they were typically encountered in forests and jungles, though some were known to adapt to living within buildings that had many pillars.
- In their first appearance "Jaculi" was stated as being both the singular and plural form of their species name. However, in the books of later editions such as Serpent Kingdoms and Tomb of Annihilation the plural form was changed to "Jaculis."
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- Christopher Perkins, Will Doyle, Steve Winter (September 19, 2017). Tomb of Annihilation. Edited by Michele Carter, Scott Fitzgerald Gray. (Wizards of the Coast), p. 225. ISBN 978-0-7869-6610-3.
- Ed Greenwood, Eric L. Boyd, Darrin Drader (July 2004). Serpent Kingdoms. (Wizards of the Coast), pp. 66–68. ISBN 0-7869-3277-5.
- Don Turnbull (1981). Fiend Folio. (TSR Hobbies), p. 53. ISBN 0-9356-9621-0.
- Frank Mentzer (January 1985). “Ay pronunseeAYshun gyd”. In Kim Mohan ed. Dragon #93 (TSR, Inc.), p. 26.
- Christopher Perkins, Will Doyle, Steve Winter (September 19, 2017). Tomb of Annihilation. Edited by Michele Carter, Scott Fitzgerald Gray. (Wizards of the Coast), p. 256. ISBN 978-0-7869-6610-3.
- Eric L. Boyd (September 1997). Powers & Pantheons. Edited by Julia Martin. (TSR, Inc.), p. 141. ISBN 978-0786906574.