There was an optional ‘make initrd’ step in the DragonFly build process, where you can create a small binary to use for mounting encrypted root drives.
Aaron LI has removed mkinitrd in favor of ‘make initrd’, which builds a separate binary to use in exactly those situations. See the commit message for more detail. It incidentally creates a ‘/rescue’ directory and works as a rescue ramdisk, similar to other BSDs, if you should ever need it. (See updated MOTD for details)