Snowman is a very basic card with low stats that is highly used in the Tutorial. This card has an ability similar to Patience's effect, being able to paralyze a monster. However, it can only activate this effect if you have less monsters on the board than the opponent.
Keep in mind that it will not work if Snowman becomes the monster that will make both boards equal in numbers. So before playing it, you must have at least 2 less monsters.