This is because this creature lets you look at your library's top card at any time and cast that spell as long as it's a Merfolk
You can flop 18 power and toughness onto the board for a mere 8 mana if you have three things you are happy to blow up
Some of them are just here to help
Due to this, I think this card is exceptionally good, since there isn't really much it's competing for a slot with

Each Collector Booster contains: An opportunity to open a card from 1994's Legends set (found in 3% of Dominaria United Collector Boosters) 1 Traditional foil Booster Fun rare or mythic rare that could have extended-art, showcase stained-glass, borderless art, or Phyrexian-language treatments 2 Alternative-border rares or mythic rares that can be showcase stained-glass, borderless, Phyrexian-language, or foil-etched or non-foil versions of the rare Legends Retold cards 1 Extended-art rare or mythic rare 1 Traditional foil rare or mythic rare 1 Guaranteed textured foil in either uncommon, rare, or mythic rare 1 Uncommon non-foil or foil-etched Legends Retold card 1 Uncommon traditional foil showcase stained-glass card 1 Traditional foil full-art stained-glass basic land 2 Traditional foil uncommons 4 Traditional foil commons, unless one is replaced by a Lost Legends card Draft Boosters Dominaria United Draft Boosters are designed for that perfect Draft or Sealed play experience, but just like Set and Collector Boosters, every single Draft Booster in Dominaria United contains a legendary creature, perfect for defending the plane from a threat to the Multiverse
