This patch changes all of the post-game unlockable boss characters for other ones from the campaign, each with their own growth rates tweaked for their character as well as unique starting inventories that try to utilise odd weapons in the game (such as the monster-effective E-rank weapons, light brand, and more); includes Fomortiis as the replacement for Lyon!
Credits:
hextator, SHYUTERz, Marlon0024 - using their Demon King animations from the Fire Emblem community github repo
Full changelog:
Caellach - Gheb, with the Beacon Bow
Fado - Vigarde, with the Brightlance
Riev - Novala, upgraded to a pre-promoted Summoner with an extra warp and Naglfar to make up for Lyon being replaced
Selena - Pablo, with Alacalibur (and a fixed inventory icon)
Valter - Tirado, with Shadowkiller
Glen - Binks, with a poison bow and swiftsole
Orson - Aias, with Fiendcleaver
Ismarie - Carlyle, with the Wind Sword, Runesword, and Light Brand (for a triple-whammy of 1-2 swords)
Hayden - Beran, with a Metis’ Tome
Lyon - Fomortiis, using a combination of community resources from the repo and some original portrait work/text setup. Doesn’t feature Ravager as I had a lot of problems trying to get it working, but the changes are still in the UPS if anyone would like to take a look and let me know how I went wrong.
As with my previous patch, I’ve uploaded this to the ModDB page for The Sacred Stones in the “Addons” section. Still can’t add links to my posts, but I’ll go back and edit them in the future when I can 
Thanks and I hope other CC fans enjoy!