So I shot a destroyer droid unit with an ion weapon.

They had 4 shields.

I had 4 hits.

Ion cancels an extra shield.

1. Can the droid player just use the 4 shields on the hits?

2. Or, must they cancel one shield first, and then apply the four hit dice? (Which leaves 1 dice left over to force a save roll.)

They must cancel one shield token for the value of your ion (ion 1 = 1 shield token). Then they can take hits on any remaining shields. In that scenario, they’d lose one automatically, could take 3 more on shields, and would have to roll 1 save. If the save failed, they’d also take an ion token.

Keep those Dekas away from Ion!