The Final Boss Became A Player is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

A game that just started closed beta testing was hacked by a mysterious AI, turning a relaxing and pleasant adventure world into an inescapable monster pit. Affected by the AI, the final boss became sentient and swore to protect its own game and return it to its former glory!