Every boss gives a chest on the first time you defeat them ever, for all campaigns. After soft-resetting, boss floors have a chance of dropping a chest on the first time you defeat them on that run.
15 level. In the beginning of the level, push yellow and don`t release until victory. Try a few times and you will win. It work not from the first try.
 "Crusaders of the Lost Idols"){kind=icon}
 "Cube Escape: Birthday"){kind=icon}
 "The First Hero"){kind=icon}
 "Villainous"){kind=icon}
 "Cover Orange Players Pack 2"){kind=icon}
 "Escape Redgrove Manor"){kind=icon}
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 "Bowmaster Prelude"){kind=icon}
 "Civilizations Wars"){kind=icon}
 "Blosics"){kind=icon}
 "Meeblings 2"){kind=icon}
 "Mystic Circle"){kind=icon}
 "Stones masters"){kind=icon}
 "Infectonator!"){kind=icon}
 "Escape the Bathroom 3D"){kind=icon}
 "Submarine Vs Aliens"){kind=icon}
 "The Chimaera Stones"){kind=icon}
 "Sacred Seasons MMORPG"){kind=icon}
Every boss gives a chest on the first time you defeat them ever, for all campaigns. After soft-resetting, boss floors have a chance of dropping a chest on the first time you defeat them on that run.