Split out from "After playing 1.4.0" feedback by NK.

"Across playing in Dollet, Deling and FH I didn't come across what these rare cards were. Is it just a % drop?"

Secret Rares currently have a 1% chance of appearing in an opponent's hand, which is too rare to notice.

Planned for v1.5.0: the chance goes up to 5%, alongside new Secret Rares being added to Balamb and Timber. We'll see how that feels and tune it from there.