Like all the other Changelings on this list, Unsettled Mariner may do its best in decks where it can benefit from other synergies
There's some upside here if you end up pitching the card you just tutored, though as with Gamble, the best bet is to search for a card that works just as well from the graveyard as it does in your hand
Lets start with Excalibur II I had to think about it for a bit, because Aettir and PriwenAettir and Priwen is a crazy card
The one weakness of Chromium is how poor he is on defense
Nissa Vital Force specifically hurt Protector as she offers a recursion effect as well while being a much more reasonable return of power for the mana
Morph is a very deep mechanic worthy of an entire column to describe its design, but as this article is already on the long side, I'll just say that the key to designing morph creatures is understanding that the mystery quality of the cards is very important