Talk:Mass Invisibility/@comment-2.10.128.52-20181017125746/@comment-2.10.128.52-20181018184043

To be accurate it's +4 thac0 penalty to your opponents if they are unable to see the invisible, and a +4 thac0 bonus to you, the latter only for the first attack.

Dragons, liches and many demons are examples of creatures able to see the invisible. They will not get the thac0 penalty when trying to hit invisible characters physically. I haven't tested whether invisible characters get their thac0 bonus for their first attack against such opponents.