Time! It was a time related ability, it didn't slows him down, it actually stole his time, making him thinks that he is slow, he just moves in a different set of time.
Since time is one of the greatest attribute there is, he could only counter it with an attribute at the same level as it, space, his mastery over spatial law might not be comparable to his enemy's mastery over its own attribute but he has something to back it up.
One of the greatest threat in the universe, a black hole, with it's presence, he managed to destroy the murky time slowly domain but he knew that this ability expends large amount of energy so he cannot activate it for long.
Unlike his other source stars, the giant black hole isn't entirely subservient to him and actually just uses him to cause havoc, it wanted to swallow everything and Shadowslash is it's ticket for this.
