Mass Killing

After killing it, he got some valuable drop items. As he glanced around the place, he noticed an altar at the center. When Ranz approached it, he found a gold chest.

As expected, when he checked it, he noticed that it was locked. Fortunately, he had a gold key with him. When he opened it, he found a skill book.

He had no idea what tier it was, but the book cover was orange in color. When he read the name and description of the skill book in his hands, he learned that it was a very useful skill. Everyone would be dying to have this kind of skill.

The book's name was ! According to the description, it refreshes all his skills cooldown right away. This meant that even though his skills were still on cooldown, the cooldown would suddenly disappear if he used this skill. If not OP, what else?