The Roving Eye may very well be the perfect sideboard card. So perfect, in fact, that it needn't always just reside in your sideboard. It's clearly a contingency card, but the three contingencies that it targets are common enough that, at least in my experience, it's almost always the first card that my Unexpected Outposts end up bringing in from the side.
The effect - a corruption check - is of course an old standard. Not only does Roving Eye force the check, though, it also gives a penalty, playing the role both of Weariness of the Heart AND giving a corruption card's worth of CPs. Someone carrying a Palantir or greater item is going to be carrying at least 2 CPs to begin with, so The Roving Eye almost always moves the check into the realm of dangerous possibility. Almost any ring you come across will also give enough CPs to make the corruption check dangerous. The card doesn't work on generic gold rings - an ability which would probably have made it too powerful, considering the 4 CPs a minion player must deal with when dealing in gold rings.
You can't bank on your opponent playing with Palantiri or with rings, which is why Roving Eye is primarily a sideboard card (unless perhaps you're playing a corruption hazard strategy). You can ALMOST bank on your opponent playing with a greater item or two, though. As with many MELE cards, its high flexibility, its ability to be used in a number of different situations, is what makes it cool. And I haven't even mentioned perhaps the most obvious use of this card - as an anti-One Ring card. There are cards that are more devastating against a Ringbearer, but if space is tight in your sideboard (you'd be surprised how quickly even THAT space fills up), The Roving Eye's flexibility often makes it the right choice.
We must contend, of course, with the card's looming disadvantages. It's not playable on a Wizard, so it won't necessarily be a game-winner for you. But if your opponent is having his wizard waltz around with Palantiri and greater items, there's bound to be other way to bring him down. Still, you can't use this card on Saruman with the Palantir of Orthanc, or Gandalf wearing the Emerald of the Mariner. Bummer.
More significantly, no one gets eliminated from the a failed Roving Eye corruption check. Just discarded. In one sense, that's big - you won't lose MPs for someone like Bilbo or Elrond, and there's always the possibility of the person showing up again, especially if your opponent plays Smoke Rings/Weigh All Things to a Nicety to bring them back to the play deck. So sure, they might come back, but it's well worth the trade off. The person who lost the check was by definition carrying something cool which they'll have to cycle back into the play deck and go get again if they really want to. In a tournament setting, where every little setback counts in spades, the difference between losing somebody to elimination or to discarding is practically immaterial. Heck, maybe you WANT your opponent's Lt. of Angmar to be discarded and not eliminated, so that YOU can bring him into play on your next turn.
The Roving Eye forces a corruption check on the person you'd probably be playing corruption on anyway, the one with the items. Its gets rid of the guy, which, from your perspective, is all that really matters. Why on earth wouldn't it be in your sideboard?
Original card review taken from : http://fan.theonering.net/morgulrats/
With the authorization of the webmaster.
The reviewing team consisted of Gwaihir (Chris Farrell), Gimli (Nathan Bruinooge), Ohtar (Charles E. Bouldin, Esq.), Radagast (James Kight), Joshua B. Grace (Beorn), Martijn Steultjens (Fram Frumgarson), Jason Klank (Saruman) and Jeffery Dobberpuhl (Wormtongue)