If takinf rozen they will readily accept lancefish and white bait , etc..will take most "meaty" frozen foods once settled and best to feed two to three times a week..
Larger ones should be no problem if feeding on frozen already..your regal should be safe as these guys carry a nasty hit of their own from their scalpels and are actually included in the journal of venomous species..one of the only other fish in there..It is thought that they collect toxins from eating cynobacteria in the wild and store this which can be released as a body slime and enters a wound when sliced by the caudal scalpels...most in capticity aren't so toxic ..saying this one reefer over on rf had a real nasty reaction to a scalpel attack from his while trying to net him recently..but a few anti hystamines and pain killers later and he was fine..apart from the verbal abuse he got from his fellow reefers,lol