"Lost World" (ロスト
This world serves as an antagonist deck in the anime utilized by Vile Ranma. In Future Card Buddyfight Ace Holy Chronicles, however, this world serves as an protagonist deck utilized by Lily K. Rockwell.
See also: Lost World (Support)
Lost World is unique from other worlds in that a player wishing to use Lost World must begin the fight with a different flag and deck, and use the Lost World flag's "Belost" ability to change their flag into Lost World, resulting in the main deck being replaced by a 30-card "Lost Deck".
Once the "Lost Deck" is in play, Lost World users harness their terrifyingly powerful cards to overwhelm the opponent. In addition to being significantly more powerful than the average Buddyfight card, Lost World monsters do not have any size, bypassing the size restriction. Cards not from Lost World that remained when "Belost" was activated can still be used for the rest of the fight.