Tammy and Teddy Hodges (Brielle Rankins and Braelyn Rankins) aren't twins in real life. However, they are in fact siblings who are actually separated by one year.
The NES fighting game Tammy Hodges and Timmy Keane play is not real and was made up just for the movie. The game is a mash-up of Street Fighter 2 and Mortal Kombat, two games that didn't exist in the year the movie takes place.
The Bill Ripken "F face" card is, in fact, a real error on 1989 Fleer card number 616.
"Original Appalachian Artworks", which is credited at the end of the movie, is the company that produced and marketed the Cabbage Patch dolls.
Before filming, Neil Patrick Harris needed to do a 14-day quarantine. Each day, he posted a funny video of how he was spending it.