Steel cards often pair well with some of the best item cards in Lorcana, which can help bring their cost down and boost their power further, and action cards that can provide a faster response to your opponents moves
Shell set you back around $865 right now, but has sold for around $120 less than that
Each one has a strong questing value that forces opponents to challenge or risk falling behind, and then once challenged and/or banished, their effects activate drawing you cards, forcing opponents to discard or return a character to their hand, and more
This isnt to say that emerald is weak, or doesnt have good cards
Not only are these card designs great on their own but, once again, I was also impressed how they managed to make the art fit into the larger sea-based theme look no further than Baymax holding a life preserver or Wasabi slicing through chains while battling waves as proof of this