Ideas for faking cloaking/partially invisible?

Since transparency is a big no no and I have a cloaking ability for an enemy type, I was wondering if anyone had any clever solutions to hiding something while still giving off slight clues to that something is there. My current shader I built sometime ago breaks on iOS naturally… my theme doesn’t really work for shadows either.

You can make cool cloaking effect using refraction. But last time I checked(a while back) it didn’t work on mobile. Maybe it does now.

I’d definitely go with refraction, the untrained eye will be able to see that something is there, without giving away what object it is completely.