They're calling it the McMuffin Farmerski, which translates to "McMuffin Farmer" or "Farmer McMuffin" (but I have to say McMuffin Farmerski works for me). It's a Sausage McMuffin (sausage patty on an toasted English muffin) but with a mustard horseradish sauce, plus cheddar cheese instead of American.
As an added bonus, they're offering it for free from June 15, 2015 to June 19, 2015 from 7 AM to 8 AM (nice, if you happen to be in Poland).
If the combo sound intriguing, it's easy enough to just order a plain Sausage McMuffin and either just add some Horsey sauce or your own blend of horseradish and mustard.