Betraying Delgado with Mathis in Starfield is a tempting choice as the Crimson Fleet head is a bit of a bastard, but it's hardly a world-shaking decision in the end. Fellow Starfield rookie pirate Mathis lays out his plan to kill Delgado and sell any information on Kryx back to Naev while you're isolated in the Lock, leaving you to either shut down his proposal or let him know you’re on board with it - for now at least. Below I've laid out the consequences of helping Mathis betray Delgado in Starfield and shutting down his proposal.
Starfield Echoes of the Past Mathis choice explained
Regardless of which option you choose, Mathis sours on his idea of betraying and killing Delgado and backs out of his own plan, so your choice doesn’t matter. After navigating your way through the prison and eventually contacting Delgado via the prison intercom in the shuttle bay, Mathis will ask you to forget about the whole “killing Delgado” thing, so there’s no mutiny opportunity while you’re in the Lock (make sure you loot the Starfield prison cell cache while you're here too). At this point, you can also tell Mathis that he owes you, although I’m not sure if this leads to anything – he is a pirate after all.
Head back to the Key and report to Delgado, then you can speak to Mathis again in the Last Nova bar. He seems pretty set on laying low and not plotting any more betrayals. While you don’t get any rewards from this exchange directly, that’s a crisis averted for the Crimson Fleet. Press on with the Starfield Crimson Fleet questline and you'll eventually reach the culmination of your undercover missions with the Starfield Kryx's Legacy choice.
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