This is a package of music containing multiple, short loops, each an additional layer of intensity, in the orchestral genre.
It is organized into an FMOD file, which can easily be plugged into Unity, and edited in real time.
Find out how easy this is here:
https://www.youtube.com/watch?v=USCJ8xU20_k
All that will need to be done, on the coding end, is that the code must tell Unity how intense the music should be. You can base this on player health, number of surrounding enemies, it's your choice.
The music is organized in a tiered system, from 0-5. Level 0-.9 is low, horror ambiance. Level 1-1.9 is ambiance + a fast, danger-evoking melody. Level 2-2.9, 3-3.9, and 4-5 are all ambiance and dangerous music, increasing in intensity. Level 4-5 adds demonic sounding whispers.
If you do not want to use FMOD, these files are perfect loops and can be used easily by Unity's sound engine to create the same effect, although it will be more work and re-inventing the wheel, so to speak.
