Sure, it sounds like something you'd see printed on Valentine's Day candy... but trust us, Keepers, there's nothing very loving about this little treat!
The U.R. Mine is a 1x1 consumable Trap, hidden until detonation, that deals heavy Fire splash damage (in a 3 tile radius) to flying targets - and other flying targets near them - that get within range. They first become available at Workshop level 7, when Keepers are able to purchase up to two Mines, for a cost of 50 Dreadstone each. Two more Mines become available at Workshop level 10. While the initial purchase of each of these Traps will require Dreadstone, subsequent upgrades to U.R. Mines (which will increase their damage) will require Gold. As they are consumable, each Mine will only fire once before needing to be re-armed.
So why such a sweet name for such a dangerous item, you ask? Perhaps it has something to do with the... "free hugs" given to your opponent's flying units? Whatever the reason, always remember, Keepers: Love is a battlefield, so arm yourselves accordingly!