Phyrexia: All Will Be One includes a single Flashback card, using that mechanic "deciduously". These present-but-not-everywhere mechanics have been normal in commander decks forever, but it's only in the last year or so that standard sets have done this.

Tim lit the beacon looking for someone to geek out on this with and Discord member LudosGD answered the call! We talk through what the current deciduous mechanics guidelines might be and then talk through how those rules apply to a variety of old mechanics.

As usual, the best way to engage with us is through Discord: https://discord.gg/t88Vpwh