To complete the Surprise! Challenge in Lego Star Wars: The Skywalker Saga, you need to trigger the secret defenses on the landing pad during the Hibernation Station level in Episode V – The Empire Strikes Back. The Challenge is completed near the end of the level, and its objective can be completed with any character.
Gain access to the landing pad by defeating the Empire officer found in the corridor east of the landing pad door (beyond the laser barrier), and taking the key card from him. Use the key card to open the door, then go through and run along the platform towards the Millennium Falcon. You’ll now have to defend Chewbacca while he makes repairs to the Millennium Falcon, just like you did during the Hunk of Junk level in Episode IV – A New Hope.
Complete the Surprise! Challenge by mounting one of the gonk droids (brown batteries on legs) near the Millennium Falcon and riding it onto one of the two switches either side of the point where the long platform meets the landing pad. This will activate a large cannon, which you can ride for some extra firepower. You can actually activate another cannon using another gonk droid, but you only need to do it once to complete the Challenge.
