When playing Diana, Scorn of the Moon with an Empowered Mel, Newly Awakened in base. Upon using Moonfall to drag a unit to a battlefield where a showdown is happening, does Mel's additional -1 Might apply to either: - Just the unit that was moved with Moonfall - Every enemy unit at the battlefield - No units at the battlefield, only the base -2 Might from Moonfall

The moved (chosen) unit gets -3, and every other enemy unit at that battlefield still gets the base -2.

Mel, Newly Awakened's empowered ability is a replacement effect that only boosts the -[M] a spell "gives to a unit it chooses." Moonfall only ever chooses one unit — the one you move. Only that unit's -2 event is eligible to be replaced with -3; the "give enemy units there -2" instruction affects all the other enemy units programmatically, so Mel does nothing to them. This matches official FAQ #11740.

The showdown context doesn't change anything — Diana's legend (Scorn of the Moon) generating energy during the showdown is just how you're able to pay for and play Moonfall at that timing. Mel's replacement applies to your spell regardless of when it resolves.