Now, if I tried to enter twrp recovery by holding power button + volume up, it would refuse to boot into recovery and just bootloop again. But, I was able to access fastboot mode (don't know why but I could easily boot into fastboot mode)
I downloaded stock ROM for Mi3 and tried to flash it via MiFlash and it succeeded but the device would still bootloop. I also attempted to flash twrp recovery via flashboot and it succeeded, again, but my phone would refuse to at least boot into twrp recovery mode, again. Naturally my phone still had the bootloop at the Mi logo, sigh.
I don't know what to do anymore, aside from sending my phone to repair center that might charge a fortune. Please help!