Tendril's Demise was a 10-page sneak peek released in 2007 as a feature for the magazine Furnation. It depicted events that were supposed to be happening several volumes in the future, estimated at Volume 7, between the protagonists and a nightmare known as Tendril. The reason for releasing a part of the story so far ahead of the current plot was to showcase characters using their powers in full combat against a nightmare.
In early 2013, David undertook a major rewrite process of the Graphic Novel Saga's story past Volume 3. In the process, one of the sequences that was left on the cutting room floor was Tendril's Demise- thereby rendering the 10-page comic uncanon and just for fun. This is noted by a major design change in the titular nightmare character, Tendril- who made his first appearance in Volume 3. It should also be mentioned that before the rewrite, fan speculation on Mace's power often cited the events in Tendril's Demise as an indicator as to what it may be. Now that it is non-canon, the comic can no longer be pointed to when speculating the orphan's power