Sapphire cards, like Aurora: Dreaming Guardian, have unique effects that can help build strategies and buff other characters
Dragonlair Spider is a 5/6 Spider that costs two generic, two Red, and two Green mana to cast, and has the Reach mechanic (can block creatures with Flying)
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They can be distinguished from non-Lesson cards thanks to the parchment and quill watermark in their top-left corners, just next to the card name
Whether its creatures that offer card draw, handy spellslinger options for Izzet (red-blue) favorites, or a focus on artifacts, theres a lot to like here
Sin, Spiras Punishment Sin, Spira's Punishment could be fine top-end for a self-mill deck that utilizes mechanics like delve or cards like Relic of Progenitus to sculpt the graveyard and give them plenty of control over what you get back