Board Thread:Questions and Answers/@comment-29414935-20180103205412/@comment-4708882-20180103215722

Mentally Ill is for those who are shown to have an actual mental illness such as being mentally handicapped, extreme mood swings or similar actions to such not simply cruel or evil people. I do believe some just abuse it due to thinking "Most people don't do this" vs genuine mental disorders.

Delusional is meant for those who actually believe they are heroes, doing the greater good or in the right. While delusional characters are fairly common plenty of villains either know they are evil or simply don't care either way. Just because someone doesn't directly say they are evil or break out in to insane laughter doesn't make them Delusional.