User blog comment:GreenMoriyama/Judaeth, Messenger of the Limbo/@comment-9155327-20160610024029/@comment-3391671-20160611005050

Although not as significant, the ult is a "Zone of the Limbo," which means that entering it already deals damage through Judaeth's innate. I believe it does its work since it becomes a zone of attrition, especially if your own team takes advantage of it to be resistant to more damage.

If you feel it's still not impactful enough, I could have the speed modifiers be a passive to anyone who enters the Limbo and let the active simply send units in and out of it (with no additional effects).