Do I need the base game to use the 600 Eclipse Credits?

Yes, you need the Marvel’s Midnight Suns game to use the 600 Eclipse Credits, as they are an in-game currency and cannot be utilized without the base game.

What are Eclipse Credits used for in Marvel's Midnight Suns?

Eclipse Credits are an in-game currency used to purchase premium cosmetic character skins via the in-game Marketplace, allowing players to customize the look of their Midnight Suns team.