The numbering of each card is different from the numbering in the main set they came from
Polukranos, Engine of Ruin adds lifelink to the mix and grows to 6/6, plus it gives you Hydra tokens when it and your other nontoken hydras die
In fact we have enough cards that make and interact with Treasures now that you can build a whole EDH deck around them, and I can bet you that Xorn is going in every single one its currently the top red card from the set at 1600 EDH decks on EDHREC, and the third most popular card overall
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My work on limit breaks ended up influencing the exhaust mechanic in Aetherdrift that, despite coming out first, I worked on after handing off the vision design for this set
(Well, if you're going to run it, why stop at one?) You do the same thing except you are no longer allowed to choose Land Tax