The Doomweaver effect is the inevitable warping and collapse of reality followed by an extensive cessation of existence in an area affected by the Dreamcatcher's anomalous alterations to itself.
Whenever something contradicts the Dreamcatcher's self imposed principles, these contradictions, whether reality or a particular existence in place, either warp to accomodate the Dreamcatcher or suffer an adverse collapse of existence leaving nothing but an endless wound of emptiness.
The extent of the harm done depends on how incongruent the said alterations/principles are to reality or entities within it - the more deviant these alterations become, the more adverse and extensive the effect is to reality and those within it. This ill and irreversable result from the reckless use of the Dreamcatcher oftentimes reach a degree that is inconcievably immense in manitude it is multiversal in scale, ending inumerable worlds and dimensions in a flash of an instant.
The Doomweaver inadvertently managed to obliterate an entire universe out of existence after bringing into existence the Void Walk ability just to gain an advantage against his malevolent alter-self Lecter.
This unfortunate event however wasn't the first. Before this particular event, the Doomweaver upon recieving the Dreamcatcher made an irreparable hole in his universe that exists up to this day.
It is clear that the disadvantages resulting from the use of the Dreamcatcher far outweighs its advantages. Unfortunately however, this does not deter the Doomweaver from using the accursed artifact - to him the sacrifice of a few other universes is nothing if he can save his own.