Noticing Newbies

Hi! My name is Agustina, I'm 22, and I haven't written in a long time but I'm getting back into it. I've been thinking of an idea for a fantasy fiction story I'm writing, but I'm having some trouble.

The story is about a species that protects the human race by collecting their negative subconscious thoughts. The main way they do this is by extracting nightmares from the most powerful dreamers before the nightmares become reality. The collector has a psychic link with his assigned dreamers, which is how he sees into their dreams. This is the problem:

I can't seem to think of a way that the nightmare is actually present in the dream. (Nightmares being dark entities that force their way into dreamers' minds in order to strengthen and be able to live outside of a dreamer's mind in the real world).

I can have the nightmare appear as a monster that the collector has to fight, but that just seems cliche

I hope this post made sense!! Any advice would be amazing!