With the ghost in a separate layer, you can play with its opacity relative to the other layers. It might also be worth tinkering around with the various layer options in "Mode" -- I have no idea what most of them do, but you can get interesting effects that way.
You can use the "Blur" or "Smudge" tools to soften the ghost's edges relative to the background. Sometimes it's just the sharpness of edges that gives something a cut-out look.
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With the ghost in a separate layer, you can play with its opacity relative to the other layers. It might also be worth tinkering around with the various layer options in "Mode" -- I have no idea what most of them do, but you can get interesting effects that way.
You can use the "Blur" or "Smudge" tools to soften the ghost's edges relative to the background. Sometimes it's just the sharpness of edges that gives something a cut-out look.