You may choose to discard your hand even if your hand contains zero cards
I have an on their way out box with a piece of paper inside with the date I last took a card from said box
Some examples: Swords to Plowshares, Teferis Protection, Chaos Warp, Great Train Heist (or other Spree cards, you pay extra costs but can go wild), Akromas Will, Deflecting Swat, Wear/Tear, and my personal favorite, Reprieve
For decks full of one or two drops, this card can be a nightmare for which they will happily trade multiple cards, as the Keg amounts to a two mana one-sided Wrath of God or sometimes even worse by killing artifacts like Cursed Scroll, Winter Orb or Ankh of Mishra
It's trademarked