Don't forget about Regenerate. Returning to 1 HP at the start of every turn is almost as good as trollish regeneration.Realistically though, the ki-rin is a force multiplier in combat. The main tactic of the beast is to keep it's minions buffed and healed, while the PC's try desperately to kill it before they end up defeated themselves. The ki-rin has very formidable defensive options for this style of encounter, including Sanctuary if need be. And swapping into spells like Mass Heal and Revivify will cause the PC's to pull their hair out. Although it will be an extremely frustrating war of attrition for the PC's, it will be a memorable boss fight for sure.