As if Mystery Killer Sudoku Pro didn't already have a long-enough name, in this Zero variant not all cages are given. Those which you don't strictly need to solve the puzzle are removed.
So put another way, you add Zero to Mystery to Pro to Killer to Sudoku.
Simple! But in fact while it's not a puzzle for beginners it's definitely suitable for anyone at all interested in Killer Sudoku and makes an interesting variation and challenge. That said, these puzzles can be very tough indeed! But guessing is never needed, and there's always a unique solution.