Monster Party

Monster Party is a platform video game for the Nintendo Entertainment System, released in North America in 1989 by Bandai. It is often considered a fairly obscure game for the console. In the 2000s the game became infamous in online gaming circles when prototype screenshots of a Japanese version of the game known as, Parody World: Monster Party (パロディワールドモンスターパーティー) began circulating online, but this version of the game was never officially released.

Story
The story revolves around a child named Mark who is on his way home from a baseball game, when he is suddenly approached by a winged alien known as Bert, who seeks assistance in ridding "evil monsters" from his realm, "Dark World". Being the first person he encounters, Bert tries to enlist Mark as his aid in battle. Mark is reluctant to help, but Bert explains that anyone will do, and that Mark's baseball bat will be as good a weapon as any. Bert quickly whisks him away, and on the way to Dark World magically fuses himself to Mark so that they are one being (with Mark able to transform into Bert for a limited time).