The licensed Lost Worlds
family of games comprises numerous gamebooks whose characters can be played interchangeably. Despite their sometimes disparate themes, they are compatible, and can be intermixed; their characters can played against one another, due to their use of the official Lost Worlds engine.
The gist of the Lost Worlds game engine is this: Each player has a picture book that depicts the various attacks and actions of their Lost Worlds character. The players exchange books, so as to see what actions the opponent is taking against them. However, each player retains their own character's Character Sheet card, which lists a menu of the character's actions, each with an associated page number. The players simultaneously choose an action from their respective character cards and announce the page number for that action. Each player then turns to the page announced by the opposing player and consults a matrix on that page which cross-references the ways the various actions interact. Each player then turns to the page designated on the matrix to see the outcome of the simultaneous maneuvers.