Mercury oil nowadays comes in the form of a synthetic blend as opposed to the generation ago when manufacturers used to fill in special oil in the outboards that would steer the process of wearing off of piston rings and bearings. As a common practice, when you buy your new engine or car, you will be very much excited to strictly follow all the operating restrictions and even want to change the oil as regular as possible, complying with the user manual requirements to the latter.
Typically, all modern outboards are formulated to accept synthetic base oils. This makes it possible to switch between mineral base stock to synthetic blends and back without causing any severe damages to the engine. This is possible and sometimes recommended provided that the oil meets viscosity standards for that specific engine.
However, mercury oil comes as a 2-cycle or a 4-cycle based on the type of engine it is to be used on. Also, remember that it is necessary to check your engine if it is a 2-stroke or a 4-stroke to enable you to determine the most suitable oil type you’ll need for your engine. Therefore, much carefulness is key in reading your user manual before doing anything to your engine.