Those tend to be the ones that people proudly display, as it means they achieved something difficult, and may have unlocked an emblem that very few other people have
In this case, the spell side provides an infinite-hand-size emblem while drawing you lots of cards, and the Sea Gate, Reborn side is an untapped mana source if needed early on
I really enjoy decks that work with a setup in which each card interacts with another, and create a big chain of effects
However, one card stands out above all others, and thats Beseech the Mirror
It has a high buy-in but Gaeas Cradle shows us how high it could theoretically get (not that a card that is multiples in Legacy is comparable in demand to an EDH card, though there are fewer Sanctums than Cradles)