I know it seems like いいな means "that's good" but in anime like Akagi and Kaiji, the narrator says いな and the subtitles translate it as "that's wrong". Is いな some kind of old phrase for "that's wrong"? What does it mean?
Yes, like Sjiveru, I wasn't sure if you meant ”良いな” or "否”. I believe that "否” is used rather infrequently. Of course, as Sjiveru mentioned, ”良いな” means, "that's good." But, of course, it embodies multiple meanings. It can also mean "That's good for you. And I'm envious." This is often used by women in a sort of whiney (and I mean that with all due respect :) voice that ends with falling intonation. It can also be used at the end of an informal meeting (like a high school club meeting) to close the meeting and confirm that all attendees agree on what's been decided in the meaning. It can also be used sarcastically.