Diana, Lunari

Does Diana, Lunari's ability resolve before or after attack and defend abilities from the start of combat?Copy Anchor Link

When combat opens with a new showdown, Diana's ability triggers first but resolves last, after all attack and defend abilities generated immediately afterward.

Start-of-showdown effects happen before units gain their attacker and defender designations, so Diana triggers before those designations trigger attack and defend abilities.^{[383.4.e][383.4.f][466.2.a][466.2.b][466.2.c.3]} These are consecutive combat-opening tasks with no priority between them, so all resulting abilities are pending on the combat chain before any is finalized or can resolve.^{[334.1][334.2][466.2.d]} The newest chain items resolve first, so the attack and defend abilities resolve before Diana's ability.^[340.1]

If combat opens during an existing showdown, the showdown does not begin again, so Diana's "when a showdown begins here" ability does not trigger.^{[466.1][466.2]}

When do I pay the 1 energy for Diana, Lunari's ability?Copy Anchor Link

You pay it while Diana's triggered ability is being finalized, before opponents receive the normal opportunity to play Reactions to the ability.^[407.4]

Because "you may" is the first part of the effect, you choose whether to perform the ability during finalization.^[383.3.a] The immediately following "pay 1 to Predict" is a cost within instructions, so the payment becomes the triggered ability's base cost and must be paid for the ability to finalize.^{[383.3.b][383.3.b.1][740.4.a]} While paying, you may activate an eligible Add ability with Reaction to provide the energy.^[445.2.c]

If you decline to pay, the pending ability is removed from the chain without finalizing.^[405.2] If you pay, it becomes a finalized chain item, and opponents may react before it resolves.^{[407.2][407.4]} When it resolves, you Predict, reveal the top card of your main deck, and draw that card if it is a spell.