Malwarebytes AntiMalware does not replace your Antivirus but it detects and eliminates malware which your antivirus misses. The free version removes rootkits and repairs the files they damage alongwith detection and elimination of malware.
The premium version has many added features. It detects malware automatically in real-time, before it can infect. It prevents access to and from known malicious webpages thus preventing your computer being invaded by malicious software released by those websites. The premium version has the Hyper Scan Mode which scans faster by only looking for active threats. It enables you to schedule automatic scans and database updates. The Malwarebytes Chameleon Driver included in the premium version prevents malware from terminating Malwarebytes or modifying its processes.