Dragon Link has been a powerful Link monster strategy in the past that utilized the Guardragon cards, while Dragunity was the predecessor of many modern synchro-based Dragon decks
With that being said, you'll definitely want to use this card in a deck if you're using restored Pokemon in your deck like Tirtouga from this set, that way you can utilize Relicanth's Fossil Hunt move and get your restored Pokemon into play faster
Let's review, it's 4 power on turn 3, check, cost reduction for any spell, check, and scales up with a good portion of your deck, you bet you should build in more such creatures
Since there is such a limited number of these premium cards, they tend to go for some outrageous prices
Here you can have the Dog play fetch whichever one is the best for the time