I have a Guide, but the basics is that you have to use the environment to herd ghosts, either siphoning a few at a time, or try rounding them all up. If you can't avoid being eaten, buffer struggling and escape, preferably from a ghost that deals less damage, then flash those ghosts and siphon them. You can also pass through stunned ghosts, and bump into them while siphoning them, even doing so right on top of them to get i-frames. Releasing them also lets you briefly remove them from the room as well.