The Pattern-blades, weapons of tremendous power with a portion of the Pattern enscribed upon them. They cut nearly anything, slice through and parry magical effects as if they weren't there, and ignite the blood of anybody with Chaos blood within them if they are nicked.

In Zelazny's canon, there are three known Patternblades:

In the Zelazny canon, the Patterblades are nowhere near as lethal as they are in Through A Mirror Darkly or The White Rose Saga, or their next-generation campaigns. While they still cause Chaosians to start burning when cut, it was not demonstrated that they could disrupt magic or 'cut anything' -- an example of GM tweaking in action.

Some additional notes on the lethality:

In [The Guns of Avalon]? Strygalldwir is struck several times with Grayswandir. Two slashes upon the chest and arm, and then being run through. The wounds flame, but the demon doesn't burst into consuming flames until it's already dead of a broken neck.

In [The Courts of Chaos]?, Corwin kills Borel by running him through with Grayswandir. Again, he doesn't begin to burn until after he's mortally wounded.

Given that the only examples we see, this could easily be examples of Chaosians burning up when wounded in any way, it's not even clear that the flames are caused by the Patternblade. It could also be that the wounds flame like a normal person would bleed, and that the consuming flames only occur on mortal wounds. Anyone have counter examples? --KeepRats/DaR