A few things to note with the cloaking, turn the diffusion and ambience to 0 with the transparency at 100, otherwise you will still be able to see the object. And if you want to have it happen instantly, then have a keyframe at frame x with trans 0, and a keyframe at frame x+1 with trans 100, otherwise it will be a gradual effect, which you may actually want.

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Ignore the shooty dog thing.