It allows you to sacrifice creatures to find nonlegendary creatures with lower mana value and put them on the battlefield
It lets you look at the top six cards of your library and then choose any two creatures that cost up to three mana and put them into play
Best card-draw cards MTG Treasure Cruise Skullclamp Brainstorm Sylvan Library Faithless Looting Phyrexian Arena Beast Whisperer Rhystic Study Esper Sentinel Sphinxs Revelation There are a lot of ways to draw cards in MTG
You can activate the mana ability of a Treasure even if you have nothing to spend that mana on
Since she brings the Grixis colors to the table as well as an instant/sorcery matters slate of themes, Kess is strong as she has access to the colors of removal, counters, burn, bounce, and card drawing
With the love of high-powered cards, theres a lot of room for interesting (often cheap) high-tougness cards to make an impact