Gray Merchant of Asphodel Which mono-black card has ended the most games of Commander
If the search is simply for a number of cards without stating a quality, you must have them find that many cards (or as many as possible, if their library doesn't contain that many cards)
Whispers in the Well - Emerald and Amber Best cards: Simba, King in the Making The Amber and Emerald deck for Whispers in the Well has an unusual gameplan - you'll be going wide with characters, each of whom has a very distinctive ability to answer your opponent's strategies
Being able to break out a thoroughly annoying black deck, though
Talking of Strength-buffing, Ruby Chromicon fits into decent range of decks as a simple tool
But anyone who's played the game, Garfield included, knows that magic itself has a much richer history than a mere deck of cards at a tournament table