These codes will often reward you with a card style, which is a skin of sorts for specific cards, or artwork for sleeves, so you can make your deck look a bit fancier
The former is almost a two-mana, no-drawback Experimental Frenzy, providing card advantage every time you can cast from your deck rather than your hand
Other cards you could add are Thassa's Oracle, Bident of Thassa, Retreat to Coralhelm, maybe High Tide, Tidal Influence, Tidal Surge, Tidal Wave, or high-toughness Crabs like Ancient Crab to hold the fort while you mill
Players can also bring their own crafted decks to the table to challenge Ursula
As for the sets themselves, unless more have appeared since TCA posted up his videos the sets themselves were not complete
Being able to use the Enlist ability and chain it into different card effects opens up a lot of possibilities for strategies including these cards