Restoring GRUB2 (Antergos)

Method One:

Boot Live CD and run the following command to determine where your Antergos/Arch/Manjaro partition is.

blkid

Mount it.

mount /dev/sda5 /mnt

Change root directory.

mount -t proc proc /mnt/pro

mount -t sysfs sys /mnt/sys

mount -o bind /dev /mnt/dev

mount -t devpts pts /mnt/dev/pts/

chroot /mnt Install mtools and os-prober.

pacman -S mtools os-prober

Install to dev/sda (or whichever your mbr is.)

grub-install /dev/sda

Update and configure GRUB

grub-mkconfig -o /boot/grub/grub.cfg exit

Method Two: 

pacman -S arch-install-scripts --noconfirm 

mount /dev/sda? /mnt (Change sda? to your own configuration for root.) 

mount /dev/sda? /mnt/boot (Only if you have a separate boot partition.)

arch-chroot /mnt

grub-install --target=i386-pc --recheck --debug /dev/sda (No partition number, just the sda/sdb part.) 

grub-mkconfig -o /boot/grub/grub.cfg

exit

Add Unknown Public Keys

gpg --keyserver pgp.mit.edu --recv-keys R2UERFFE8DDFZ9