While Graaz is a steep 8 mana, and its colorless identity means you have to omit a full 10 myr from your card pool, its just about the best way to turn your myr into lean, mean, juggernautin' machines
As a player who cares primarily about Underground Sea as a game piece rather than as an investment, a few dings, scratches, or an artist's signature probably aren't a big concern
7 Ancestral Recall Beta Edition - $15,000 From the 1994 Beta Edition, this card was sold on September 30, 2020
The most obvious option, by far, is using the Fling spell to instantly eliminate any defending opponent by throwing it right at their face
Its also the sort of threat thats nice to have at the top of the curve for a Sacrifice deck or as a solid threat in midrange builds of Reanimator that plan on casting their creatures some of the time
2 Mind Flayarrrs - Draining Sanity Mind Flayarrrs plays into Magic's cards-equals-intelligence theme by assembling a group of eldritch Horror creatures that cause players to mill cards whenever they deal damage