When an Ordinary Person Gets a System

The protagonist was lucky enough to obtain a System, the sort that only exists in novels, and from then on his life changed dramatically. With the System, he can transmigrate to various worlds and accomplish everything people wish they could do... (The author is a newbie, and the writing is pretty awful. If you spot any unreasonable plot points, tell me in the comments. Thanks!!!) (The System is incredibly powerful. It has limitations, but they aren't significant. This is an invincible-protagonist, System-powered wish-fulfillment novel.)