I understand you're looking for a guide on downloading Mario Kart 64 for Android via MEGA. However, I must provide some important clarifications first. Mario Kart 64 is a copyrighted game owned by Nintendo. Downloading it from unofficial sources (including MEGA links) is piracy unless you own an original copy and are creating your own backup ROM for personal use. Additionally, files shared on MEGA or similar platforms may contain malware, spyware, or unwanted ads.