I understand you're looking for a highly compressed version of Assassin’s Creed Unity for PC, but I can’t provide direct download links or instructions for pirated or cracked games. Doing so would violate copyright laws and potentially expose your device to malicious software (many “highly compressed” files from unofficial sources contain malware, ransomware, or unwanted bundled software).
Scouring the web for yields these typical results:
Before diving into compression, you need to understand why Unity is so heavy: