This effect is granted by the item Erebrandir's Horseshoe.
The following was posted by Sapience on 11 October 2012: Erebrandir's Horseshoe - What is it good for?
- Erebrandir's Horseshoe - What is it good for?
- "As promised, the full text of the message regarding Erebrandir's horseshoe...
- "It's time to pull the veil back just a bit on the mysterious Erebrandir's horseshoe and what it does.
- "For starters, it does do something. Some may think it doesn't, but it does! In fact, it does more now than when it was first introduced. This is why we've kept its effects a closely guarded secret. As time goes on, it grows more powerful! So when should you be using it? Some portions of the Epic story and certain festival events benefit from having this lucky horseshoe. In fact, the winter festival would be a good time to dust it off!"
And later in the same thread:
- "And it does reveal several things. And with a little thought it should actually tell you quite a bit about both what it does now and will do in the future (that's another tip off BTW)."
The following was posted by Sapience on 19 August 2013: 
- "Three pretty clear examples(about the post above). Also, as we've said many times, It changes. As developers add new things to it it does more. So to say it does "X" would be untrue. It does impact a portion of the epic story (which is where you get it remember), and the winter festival, and some other things and probably more that I am not aware of.
- "As for what players think it does (based on that site). False."
And later on 20 August 2013: 
- "I didn't say 'quests' I said quest. It changes exactly one line of text in one quest in the same Epic line that you get the horseshoe. This was its first, original use.
- "To be clear, it doesn't make any major changes to the outcome of anything. Though you may want to use it if you're ever in a snowball fight."
It has been suggested that equipping the Horseshoe might:
- improve fishing.
- affect loot from chests.
- improve your chance of getting on stage in the theater at Frostbluff.
- increase the crit chance for Relic combining.
- improve your chance in the Treasure Hunt event.
- One of the dwarves in the Treasure Hunt suggests to take something lucky into the fields, saying that "one should always carry a lucky item in their pocket, like a horse shoe."