If you’re going to chroot manually, then you need to make sure that /dev, /proc and /sys are mounted in the target root filesystem before chrooting into it. And if it’s a UEFI-native operating system, then you also need to make sure that /sys/firmware/efi/efivars is mounted as well — device efivarfs and type efivarfs.
/dev can be bind-mounted from the source, but the others have to be explicitly mounted with the syntax… 
mount -t type [-o options] device mountpoint
manjaro-chroot does not work with btrfs. A manual chroot is the only option there. It’s doable — I’ve already done it myself a few times — but you have to know what you’re doing. 