Worlds Collide is a convention in New York that features the combination of The 39 Clues, Infinity Ring, Spirit Animals and more recently TombQuest. It has also an internet counterpart, including games, activities and an e-book.
The first Worlds Collide event happened in 2014. It only featured Infinity Ring, Spirit Animals and The 39 Clues. The e-book released that year was called "Tales from an Awesomesauce Party".
The second Worlds Collide event happened in March 2015. This one also featured TombQuest, the newest multi-platform series.