This is an extended example of the original Cave Bridge (https://editor.construct.net/#open=cave-bridge) with the ability to jump. The stones can fall off now on collision with the player. But not entirely off the screen.
An implemented condition (BridgePiece.Y>1000 ? BridgePiece.Y-3 : BridgePiece+3) prevents increasing the Y coordinate of the stones over 1000.