This is the Double Exposure Embedding for SD 2.x.
It was trained with the v2.1 768 ema pruned model on 768px images of people, layered with a variety of surroundings. It's been shown to handle objects and animals good as well.
Place the file in the embeddings folder of your Automatic1111 installation.
Trigger the effect in the prompt by writing dblx.
Read more and get more prompts for sample images on the Hugging Face page.