Banned?
Most people in tournaments would be happy to see Yogg in their opponent's deck, because it is completely unreliable and more often than not is a detriment to the person playing it, due to the full turn invested late game. Yogg is 100% an "I am about to lose, lets see if this gives me a second chance" card, nothing more, and because tournament decks favour reliability and stability over RNG it will never be a strong tournament play.
For every time something like that happens, there are four times where Yogg fucks its own player.