Ysalamiri, approximately 50 centimeters in length, were arboreal, lizard-like beings indigenous to the planet Myrkr. They are best known for their unique capability to repel the Force by generating a zone of Force-neutrality. The reason for this ability's evolution was as a defensive mechanism against predation from the Force-sensitive vornskrs. When many ysalamiri congregated, their Force-neutralizing field could extend across various distances, sometimes reaching kilometers.
Fully-grown ysalamiri attained a size of up to 50 centimeters and reproduced by laying bubble-like eggs.
Ysalamiri would embed their claws into the Olbio trees they inhabited, from which they derived sustenance. It is theorized that the substantial presence of Mandalorian iron within the Olbio tree leaves played a role in the ysalamiri's Force-dampening properties. Extracting a ysalamir from its host tree was exceedingly difficult, often resulting in its death. Nevertheless, Talon Karrde's smuggling organization discovered a method to do so, which was subsequently adopted by Grand Admiral Thrawn. Thrawn strategically employed ysalamiri for protection by affixing them to a harness worn on his back or a nutrient frame. This allowed him and his subordinates to remain secure within the Force-repelling field of the ysalamiri. This tactic was used to attract the attention of the cloned Dark Jedi Master Joruus C'baoth, also to expedite the Spaarti cloning procedure, avoiding the typical adverse consequences (which arose from the interference of similar Force signatures).
Ysalamiri did not truly nullify the Force; given that all existence is imbued with Force energy, such a feat would be impossible. Instead, they emitted a field wherein individuals were incapable of manipulating the Force. The area of effect for an individual ysalamir was roughly 10 meters in diameter; larger aggregations of ysalamiri could amplify their combined field to span kilometers, but this required a significant number of creatures.
Miriskin was a product that was rumored to be created using ysalamir hide.
The Jedi Order, holding the ysalamiri's resilience in high regard, adopted the creature's name for a style of lightsaber combat known as Makashi.
Tyber Zann was known to keep ysalamiri captive in cages as a way to limit the destructive potential of Force wielders.
Ysalamiri were initially introduced in Timothy Zahn's 1991 novel, Heir to the Empire. According to Zahn, the concept of a being capable of hindering a Jedi's connection to The Force was his initial inspiration for the narrative. This came after his agent informed him of the opportunity to author a series of books continuing the Star Wars saga following Star Wars: Episode VI Return of the Jedi. The author initially faced numerous complaints from readers regarding Thrawn's explanation in Heir to the Empire that ysalamiri could "push back" the Force. The complaints were based on the fact that the Force was generated by all living things and therefore couldn't be "pushed back" in that way. He would clarify that Thrawn's explanation was inaccurate and ysalamiri simply supress the level of the Force present, a distinction that was later shown more clearly.
In Wizards of the Coast's Universe expansion for their Star Wars Miniatures tabletop game, the Thrawn miniature is depicted carrying a Ysalamir on his right shoulder. He is unique in possessing an ability named "Ysalamiri," which prevents characters within a six-square radius from expending Force points or being targeted by Force-based abilities.