St. Patrick's Week
This item is unobtainable. They are located at the end of one of the eight BLARNEY worlds. During St. Patrick's Week you may kiss each of these stones once each day to receive a Blarney Pebble and a random St. Patrick's Week prize.
For the first Blarney of the day, you will also get a bonus prize. (or random)
You don't actually 'kiss' it, you just walk up to it. You can only kiss one stone in one world every day. That adds up to eight pebbles a day.
Upon completing all eight Blarney worlds in a single day, you will receive a Lucky Horseshoe.
The Blarney Stone appears to be a stone with a sign saying 'KISS ME' attached on top of it.