My list of ideas:
-A giant hole appears in the lobby for no reason and going down it brings you to a magical forest with a teleporter at the end to bring you out of it.
-You can see jet fighters fly overhead, some of them preforming air tricks like aileron rolls
-Men in sunglasses and black suits surround a random player and captures them, bringing them to a Half-Life-inspired room where the walls close in on you. If you can escape, you are awarded with a small unit bonus, rad sunglasses and a black suit.
-Air pirates jump down to the lobby from an air ship. They begin stealing the props from the many stores.
-An air ship steals the ferris wheel. If you are on the ferris wheel at the time, you are given a parachute and you have to jump down to safety. Players that were on the ferris wheel at the time are given a small unit bonus for the inconvenience.