@ChrisTopherGautamHota, yes, success is always sweet.
{A bit surprising that the DVD/ISO's "Apple standard" EFI bootloader path wasn't automatically detected. However, I just tried a quick test by attaching my SL Install (whole-)disc image [admittedly not strictly an ISO, but rather a UDZO dmg] to one of my SL VMs and starting it up, but then saw the same symptom too, i.e., an unexpected drop into the EFI Shell. I seem to recall that this disc image used to automatically boot before? Stranger yet is that even after detaching that disc image, on startup the SL VM still continued dropping into the EFI Shell, and I ended up having to bring up the EFI "manager" menu (by typing 'exit' at the Shell prompt [or could have kept pressing almost any non-modifier key at VM startup]), then using 'Boot Maintenance Manager' > 'Boot Options' > 'Change Boot Order' to move the 'EFI Internal Shell' entry back to the bottom, below the CD-ROM and Hard Disk entries. Anyway, all's well that ends well.}
Also, @granada29, thanks for the reminder about the CPU power management kext! Actually, I just remembered (for the umpteenth time) that many years ago former moderator @socratis had set up a "summary" thread for OS X guests '
Status of OSX on OSX'. It may be quite a bit out-of-date now, but it did discuss deleting / renaming that particular kext, and might still contain other useful advice for older OS guest VMs.
There are other threads too {esp. over in the '
Mac OS X Guests' forum} that mention additional tweaks for older OS guests. E.g., my two SL guests' system clocks tended to drift far out-of-synch with my host Mac's, and I found a tip in one of those threads about using the VBoxManage tool to apply a VM extra-data setting for timer adjustment {there's also a formal discussion about this in
the VBox User Manual, Ch. 9, § '9.11. Fine Tuning Timers and Time Synchronization'}. For my SL guests, I've set 'VBoxInternal/TM/WarpDrivePercentage' to 93, although it's not perfect and in any case that value could be specific to my particular setup.
The VBoxManage tool is also officially used to set the display dimensions for macOS guest VMs, as discussed in
the VBox User Manual, Ch. 3, § '3.14.1. Video Modes in EFI'. Oh, and of course these older OS guests can't use (the relatively limited macOS edition of) Guest Additions in general anyway, so usually there'd be no shared clipboard, etc.; however, in various existing threads @granada29 has discussed a screen-sharing workaround for that.
