The phrase "element of surprise" refers to something that is unexpected or unforeseen, often used in a positive context when describing an event or situation that catches someone off guard in a pleasant way. Full definition
Plus the added element of surprise on the back of these block heel sandals! (closetfullofcocktails.com)
Depending on your product and services, sending little gifts of appreciation with elements of surprise and delight to your best customers can be a superb means of telling them to come back. (entrepreneur.com)
Using elements of surprise, suspense, and humor works well when you want to retain a learner's attention, especially when the topic of discussion is less than interesting. (elearningindustry.com)