Urza's Command can drop the power of other player's dorks out of nowhere, make a Powerstone, make a tapped Construct token to win the game, and then scry and draw, so I think that the Construct and scry and card draw are the default here, and that's pretty good for four mana instant speed
Exiling graveyards in EDH is also super relevant, adding to the cards power
The ultimate status of a top-tier Leader relies heavily on mechanical synergy, card pool compatibility, and resource efficiency
O-Naginata (2XM foil 50, SOK foil $5) I wish there was a sweet version of this to go after, but again, adding three power is where both legends are happiest and this time it is as cheap as can be, no need for ways to cheat the equip cost