Ok, so we know they are afraid of water and fire, but what about something like steam?
Or exorcism. That’d give them the heeby jeebys, for sure.
So, two Wringwraithes walk into a bar… They get to drinking, and after a while one Wringwraithe says to the other, “Hey, you ever notice how we keep having problems with running water? Like how we’ll be chasing some guy for miles and miles, and almost catch him, but then he makes it across a stream or river or something and we’re screwed! What’s up with that?”
The other Wringwraithe says, “Yeah, now that you mention it, that is kind of messed up. We’re these awesome undead killing machines, and we keep losing our prey on account of running water. What do you think we should do about it?”
So they think about it for a while, and suddenly the first Wringwraithe says, “I’ve got it! We’ll build… a boat!”
Second Wringwraithe says, “A boat? Are you nuts? We can’t carry a boat around on horses!”
First Wringwraithe says, “No, I swear, it’ll work. Seriously, the elves make these really light, strong boats that they can port around with them; all we need is something similar. Then the next time some guy tries to lose us by crossing a river, we’re golden!”
Second Wringwraithe says, “I dunno… I never built a boat before.”
First Wringwraithe says, “Me neither, but come on, we’re both smart guys, we can do it! Let’s give it a shot.”
So they decide to work together, and they draw up plans for a really compact, portable boat, and they craft it themselves out of really light, strong magical wood.
Next time they’re ordered to go chase someone, they bring it out all packaged up, and the Lord of the Wringwraithes is all, “what the hell are you two idiots up to?” And the two Wringwraithes just smile and say, “Just wait and see.”
So they go out to find their quarry, and they chase him all up and down the countryside, and at last they’ve almost got him, but he just barely manages to make it across a river. And the other Wringwraithes are all, “Damn! Not again! Why does this keep happening?”
But now, the two Wringwraithes smugly bring out their boat, and they unpackage it and put it together. As the other Wringwraithes watch, they both drag it to the riverbank, and they lead their horses into the boat, and they shove off, and the boat immediately falls to pieces and sinks to the bottom of the river.
And the moral of that story is:
Two Wrings don’t make a wright.
Is it stalking if I seem to follow you around the board and applaud your genius?
You did it again. Awesome! 
Jim
Best to let that punny story sink like a stone, out of sight…