A multifunctional engine brake, comprising an engine valve motion transformation mechanism, a slow seating mechanism (250), and a timing oil control mechanism. By axially moving a roller (235) on a roller shaft (231), the connections between the roller (235) and different cams (230, 2302) are switched, so as to implement the transformation between different engine valve motions. A roller axial driving mechanism (100) is disposed in the roller shaft (231), thereby achieving a simple and compact structure, a symmetrical and reliable force, and easy manufacturing and assembling. The timing oil control mechanism provides timing oil supply or discharge for the engine brake, thereby eliminating the randomness of the opening or closing of a conventional engine brake, avoiding slipping and impact of the roller during roller translation, and improving the reliability and durability of the brake and engine. The slow seating mechanism (250) effectively reduces and controls the seating speed of the valve, thereby eliminating the compact within the mechanism. The brake can be used for different types of variable valve motions, comprising valve motions generating 4-stroke braking, 2-stroke braking, or 1.5-stroke braking.