User blog comment:EHeroMatty/Buddyfight's official "Irregular" Restriction list/@comment-33367792-20180503000940/@comment-28173866-20180503061211

That is simply because of Bushiroads selling strategy. Current decks get heavily oversupported until a new one pops up. After that, the support drops nearly to 0 to render the old decks uncompetititve so people have to buy the new cards. That leaves a whole lot of players, who actually like their decks, frustrated and angry, because they can't play anymore the way they want without getting their bottoms kicked.

In my opinion, the first really ban worthy card was Balle Soleil. He is cheap (gauge wise), has an extremely good set of skills with a wide variety and excellent stats. Not to mention the support in form of Dragon Force and others.

And actually, season 1 had a much greater deck variety than 3 and 4. There were always at least 2 fighters for each world, except Ancient and Hero World, with more or less competitive decks. After that, they focused on their 3 (resp. 2 in X) main decks, the villain deck and 1 or 2 other decks with little half-life periods.