So lets have a table with the options for the last slot, of which there are many
While only a preview has been shown so far, The Pokmon Company is expected to more details, preorders, and special event tie-ins very soon
Sliver Queen+Mana Echoes: The classic, will generate infinite mana and Sliver tokens, combine with a haste sliver for an infinite attack or use Lavabelly Sliver for infinite target damage and life
What we really need are one or two-card engines which can spit out hoards of treasure every turn, whether through easily-repeated triggers or sometimes a single huge lump sum
Elrond, Master of Healing FromTheShire: In said scry deck, this does a pretty decent job of slinging counters around and pumping up the team, and then if things are hit with spot removal they at least replace themselves which is useful for creature heavy decks
You may reveal a noncreature, nonland card from among them and put it into your hand