World Collide, codenamed pre-reveal as The Reckoning, is a twist that ended Survivor: Solomon Islands prematurely, and merged the nine surviving castaways with the seven remaining houseguests from Big Brother 11, into a new special event season known as Turney vs. Suitman: Worlds Collide, which featured the formats of Big Brother and Survivor meshed together.
Throughout Survivor: Solomon Islands, a major twist known as 'The Reckoning' was announced to be taking place in the late stages of the game. On June 13, 2016 - Day 14 of the season - the twist was revealed by it's actual name, 'Worlds Collide'.
During the pre-merge phase, a tribal immunity challenge would keep one tribe safe for the week, forcing the losing tribe to compete for Head of Household and Power of Veto, to avoid being nominated and evicted by their own fellow tribemates.
This changed at the merge, where the game would switch between solely Big Brother days and solely Survivor days. Big Brother days would feature HOH, POV, noms and eviction only, while Survivor days would just feature an individual immunity challenge, and a group Tribal Council.