@ Seraphic - Actually, they really don't wreck Shuckle too bad, here's an analysis for you using my Shuckle:
Froslass, Will usually just taunt you so you can't do anything. True, Shuckle loses if it Taunts and you have to switch out, but Tauntless (if there is such a thing) Froslass, or those who forgo Taunt and just use Spikes will get Encored, allowing you to Power Trick. It's usually best just to switch on turn one however.
Uxie, Can't do a damn thing to you. If he sets up Stealth Rock, he is promptly Encored, and then Shuckle is free to Power Trick and proceed to 3HKO Uxie, or severly damage any switch in that is not physical. Sure a 3HKO may not seem like much, but your opponent will probably not risk switching out once you have Power Tricked, and then you've gotten rid of Uxie with only having set up Stealth Rock. If it's a dual screen lead, it too is just encored on either Reflect and Light Screen without the ability to set up the other screen.
Ambipom, Shuckle takes about ~5% from Fake Out, and Ambipom isn't doing much of anything. This situation is a stalemate really. Shuckle can't Power Trick, so you can just Encore him if he decides to attack, or he can just U-Turn out. If he has Taunt, Shuckle is forced to switch. Not the best situation, but Shuckle will always come out alive, so he's useful later when you need to Encore something.
Moltres, is dead. Fire Blast, at the most (assuming Life Orb and Modest nature), does between ~58%- 68%. Which means, if Shuckle Power Tricks on turn one, Sitrus Berry will activate, allowing Shuckle to take another Fire Blast on turn two, and OHKO Moltres with Rock Slide. Sure, Shuckle is dead meat afterwards, but your opponent has a dead Moltres.
Alakazam, will probably Trick something on you, or Taunt(?), however, you will then Encore it's Trick, or be forced out due to Taunt. It's relatively easy to set up on Alakazam with Power Trick as Shuckle can play the same game with Alakazam as with Moltres, and proceed to OHKO with Rock Slide or Earthquake.
Electrode, will probably Taunt in your face, however, if it Rain Dances, you can Encore Rain Dance. This situation isn't the best as the likes of Gorebyss and Kabutops will OHKO Shuckle with their respective attacks when they switch in. As with Ambipom, not a lot will happen to either Electrode or Shuckle, but your opponent may be in a better position with Rain Dance set up.
Omastar, the best idea is to just use Encore. Odds are it will just be stuck on one of the Entry Hazards. Shuckle doesn't fear Surf either as it only does ~49%- 59% allowing Sitrus Berry to activate, and then you're facing a hapless Omastar that is stuck on Surf. Switch appropriatley.
Hippopotas, can't do anything to you, so just Encore Stealth Rock; however Shuckle can't use Power Trick as Earthquake will become a OHKO if it breaks out of Encore. Sure it gets Stealth Rock up, but it's hapless as well, and can't Yawn or Earthquake any other member of your team.
Rhyperior, just Encore and switch appropriately.
Cloyster, same ordeal as with Omastar. However, it is easier to Power Trick on Cloyster as Surf can only muster a 3HKO on Shuckle with Surf, and Rock Slide is a 2HKO after Power Trick. Odds are it will be stuck on Spikes after the Encore.
Arcanine, not a threat at all. Shuckle can't Power Trick, but Encoring whatever it uses is always helpful.
Venusaur, will put Shuckle to sleep with Sleep Powder. Shuckle loses, but, hey, it slept your Shuckle, not your Moltres or whatever.
Hariyama, Fake Out does little damage again, and Shuckle can just Encore Close Combat allowing whomever your Hariyama counter is a "free" switch in.
Kabutops, Shuckle doesn't like Kabutops, but again, Encoring whatever it uses is always useful.
Snover, not a threat, but Power Tricking is not recommended as most are physical. Once again, Encoring whatever it decides to do is always useful.
In conclusion: True, Shuckle can't do a lot to most of the leads, but they can't really do anything back either. And, Encoring anything is always useful. And as I said, it's really easy to bring Shuckle in later in the battle as well with the help of Sitrus Berry, and the ability to Encore any stat-uppers and proceed to Power Trick. This Shuckle will always beat Raikou, Mismagius, Houndoom and most other special sweepers as well as stop any other walls cold with Encore, (i.e. Registeel, Chansey, etc.) And I'll say this again, Shuckle is not OHKO'd by
anything in the UU tier, (besides a Life Orb, Modest, Rain Boosted, Gorebyss Hydro Pump, or something of the sort.)