RE: ♦ Special Rotated Review: Spiritomb (Arecus #32) {5/19/12} ♦
This one card is the most important reason I wanted an Arceus-on format. (Oh, and Arceus.dek. That would be fun.)
Why? Okay, let's see. Item-Lock. That is crucial. It might become the common lead in a plethora of decks, as well as radically change what builds would be like (a lot of decks nowadays are very item-heavy, and Spiritomb just wrecks that). It even gives evolution decks a fighting chance; you can evolve 1 of your own Pokemon at the cost of 10 HP...and now with Skyarrow Bridge around, he has great mobility; no Moonlight Stadium or Unown Q necessary.
Okay so 60 HP isn't all that hot, and a lot of the metagame is run by big basics, but like I said earlier, with Item-Lock and quick evolution, it gives decks more of a chance, ESPECIALLY stuff like VVV - given how Vileplume decks already have slow setup times.
Spiritomb also prevents Catcher killing, and although you can Catcher kill a Spiritomb with relative ease, you have to lock yourself for the rest of the turn to do so. Honestly, were this card around, the meta would be drastically affected...not as big of a margin as some people might think, but still pretty big.