Nexon is typically known in the wider gaming world as the developer behind Maplestory and Dungeon & Fighter (or simply DNF), though in terms of fighting games, they are also one of the publishers for DNF Duel, with their subsidiary, Neople, also being credited as one of the development studios on it.
Their MMOs are not typically known for the best monetization practices, but not many people probably expect this news. The Korean Fair Trade Commission hit Nexon with an 11.6 Billion Won fine for manipulating the drop probability in one of their loot boxes in Maplestory without communicating it to the players, resulting in the largest fine of this type in history.
If that seems excessive for a one time problem, you're right, maybe? Because the issue goes deeper than that with KFTC claiming that Nexon has been doing this for at least 10 years, and have done so maliciously, as they clearly omitted it in their regular updates.