I don't think The Decreator can even be fought, really. It's kind of like another aspect of The Original Darkness/Great Evil Beast, considering it's supposed to be the shadow of the Presence.
The Doom Patrol actually failed to stop it, but Crazy Jane figured out how to create a transmission that would interfere with it enough to slow it down, so the universe continued to get decreated slowly over the course of the life span of the Earth, resulting in only the odd lost object or missing person.. But she had prep, and information that Tyrant would be lacking.
Tyrant gets decreated.
