Marrow-Gnawer is the archetypes beating heart: all your Rats gain fear (nearly unblockable), and you can tap-and-sacrifice a single Rat to create X tokens equal to the number of Rats you control
Being a Lesson doesn't impact what the card does, but because it has that subtype, it can be cast for just one mana if you control Uncle Iroh, a Creature that makes your Lesson spells cost one mana less
The upside is that Orb can also go in decks that want to mill themselves for value, like Muldrotha, the Gravetide and Teval, the Balanced Scale
Now that we've got the new mechanics out of the way, let's get into the real meat and potatoes of the set with all the other cards
Scammers are getting better at making cards look real, making it harder for collectors to tell the difference
Cards like Murder, Abrade, Pacifism, Frost Lynx, and Rabid Bite will be your best friends when the time comes to deal with a creature