When that mana is spent to cast a red instant or sorcery spell, copy that spell and you may choose new targets for the copy
Some popular cards in a Wilhelt, the Rotcleaver deck might be: Diregraf Captain Rooftop Storm Death Baron Gravecrawler Lord of the Accursed 11 Edgar Markov ($40.79 Market Price on TCGPlayer) A Powerful Vampire Lord Who Doesn't Even Need To Be In Play Edgar Markov is the king of the Vampires typal Commander deck
Not only that, but for four mana, two of which is green or blue, you can put the top two cards of your library into your graveyard, then an opponent gets to choose a nonland card to take from your graveyard and put into your hand
I gave the creature a decent body, a 3/3 flyer, because I wanted the fact that you were giving away the creature to mean something
Hitting any permanent with mana value 4 or less removes a significant portion of threats
Magic has a rare distinction among games, in that for many players it has become a lifelong preoccupation