Your opponent will have no way to prevent the damage coming to them, plus its doubled until end of turn
Jim Davis has a good take on this
The thing is, Slivers arent actually all that popular in Commander circles, with just 800 decks or so registering the card
The likes of Waste Not, Harmonic Prodigy and Jeskas Will can help you get Kefka flipped quicker, by adding mana and doubling up on hand attack
In this article, I recount my year-long journal exploring this format, describe my hunt to acquire cards and assemble and field a tournament weapon, and then describe my unforgettable and historically significant experience competing in a major Alpha 40 tournament, dubbed The Wizards Tournament II. Organized by Magnus De Laval, the organizer of n00bcon, the Old School World Championship, the Wizards Tournament was a side event held in 2018, and received far more interest and players than initially imagined