Tamiyo, Inquisitive Student (Tamiyo, Seasoned Scholar)

Tamiyo, Inquisitive Student has been out for a while, and revealed itself to be one of the most  successful commanders available in the current metagame. The deck, however, poses two different problems: first, it appears that the deck has a better overall matchup than any other control deck against most of the other decks from other archetypes. Second, and more specifically, it also has an overwhelming matchup against other types of control decks. The combination of both of those points means Tamiyo, Inquisitive Student, while being one the best decks available, also has become the one best choice for control decks, reducing diversity and leading to poor gameplay experience.

Moreover, its unique structure, being a control deck led by a one-mana commander, creates gameplay patterns where having a turn-one removal is a necessity, reducing the strategic interest of games as well as deckbuilding options, while forcing every deck to play a certain density of such interactions.

For those reasons, Tamiyo, Inquisitive Student is now banned as a commander only.