So you know what is popular
For example, Sarkhan, the Dragonspeakers first loyalty ability turns it into a dragon until the end of the turn
Free price-check apps can be fine for occasional checks, but they are often weak for serious eBay workflows
Monoblue decks ditched Jayemdae Tome completely once this bad boy came around, and started moving towards Man-o'-War and Boomerang-style board control to set up enough time for the Ophidian to give them a hand full of cards
My biggest complaint with Guilds of Ravnica was the lack of options (and accordingly, replayability), and more alternative strategies is a great potential step towards fixing that in Ravnica Allegiance
However, all the other secret missions don't reward new cards, so the only way you'll discover them is by completing them yourself or hearing about them