The clash known as the Battle of Devil's Crevasse unfolded during the Second Imperial Civil War, specifically in the year 137 ABY. Its location was Devil's Crevasse on the aquatic world of Dac. This conflict pitted the forces loyal to Darth Krayt's Galactic Empire against the Mon Calamari Rangers, who received assistance from Master Treis Sinde of the Imperial Knights. Ultimately, the battle concluded with a victory over the Sith and the demise of the aquatic beast known as the Sea Leviathan.
Darth Krayt, the individual holding the title of Dark Lord of the Sith, issued an order for the genocide of the Mon Calamari species. This was enacted as punishment for their support of Galactic Alliance Remnant Admiral Gar Stazi, especially Gial Gahan's involvement in the Alliance's theft of the Imperious-class Star Destroyer named Imperious. Following the initial massacre targeting the Mon Calamari Council, the surviving Mon Calamari were forced into labor camps, where many succumbed to disease and starvation.
However, some Mon Calamari succeeded in escaping into the depths of the planet's oceans. To continue the genocide, the forces of the Sith Empire deployed a fleet of underwater vessels with the intent to eliminate all of the refugees. However, the Empire faced multiple engagements with the planet's native resistance fighters, the Mon Calamari Rangers. The Rangers gained an ally in the form of Imperial Knight Treis Sinde, who served as both a warrior and a strategic advisor for one of the Ranger units.
To escalate the genocide, Darth Wyyrlok suggested to the Sith Scientist Vul Isen that he should engineer a Leviathan capable of underwater movement. Acting on this advice, Isen successfully created a Sea Leviathan. After demonstrating its destructive capabilities by unleashing it upon one of the work camps, Isen and Darth Azard, the Sith Lord overseeing the genocide, deployed with the Leviathan to hunt down and exterminate the Rangers, setting course for a location where an Imperial unit had previously been defeated by the Rangers.
A patrol unit of Rangers unexpectedly encountered the Leviathan, and only a single survivor managed to escape and warn the others. While Tanquar, the leader of the Ranger unit, advocated for an immediate confrontation, Master Sinde advised against such a course of action. The Sith were intentionally directing the Leviathan towards a group of refugees in an attempt to lure the Rangers into a trap where they could be eliminated. Following a brief debate regarding the situation, Sinde devised a plan to counter the Leviathan.
As anticipated, when the Leviathan and the transport carrying the Sith arrived at the Rangers' base, the Rangers emerged to engage them. However, to Azard's surprise, the Rangers focused their attack on the transport ship rather than the Leviathan itself. Isen dismissed this tactic as foolish, given that the Rangers' Krakana underwater fighters were not designed to destroy the transport. Azard issued the order to open fire on the Rangers.
Simultaneously, the Leviathan attacked the refugees and the Rangers who were escorting them to safety. At that precise moment, a massive swarm of devilsquid emerged from a nearby crevasse. Instead of attacking the Mon Calamari, the squid converged on the Leviathan, having been commanded to do so by Sinde. The Imperial Knight also joined the assault on the Leviathan.
Upon realizing that the Leviathan was in danger, Azard ordered the transport to deploy its fighters to engage the Rangers while the transport itself attacked the squid. However, when the shields were lowered to launch the fighters, one of the Rangers piloted her vessel directly into the hangar, triggering an explosion that destroyed the transport and caused its command section to sink to the ocean floor. Meanwhile, Sinde was rescued by another Ranger while the Leviathan was dragged into the squids' lair within the crevasse, where it was presumed to have been devoured.
Isen and Azard, who were both inside the transport's command section when it was destroyed, survived the explosion. However, Azard was restrained to a chair. Isen seized Azard's lightsaber and used it to release his fellow Sith, much to Azard's surprise.
Sinde later communicated with his Emperor, Roan Fel, informing him that their forces should prepare to counter Leviathans should the Sith deploy more of them.
This particular battle was depicted in Legacy (2006) 33, a comic published in 2009. The story was penned by John Ostrander and illustrated by Omar Francia. It served as the second and concluding installment of the Star Wars: Legacy story arc titled Fight Another Day.