mtg are showcase cards legal Enlightened Tutor (showcase) reveal it Fierce Guardianship Showcase P Avatar:

Belakor doesnt help you ramp to your demons, but it does give you a massive wincon in the command zone, and being a Grixis commander gives you access to blue, which means you can use some of the cheaper, powerful blue-touching demons from 40k like Exalted Flamer of Tzeentch

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While Prosper and Rocco benefit from Junk, it doesnt seem that any commander benefits from exile play in this set

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Milling a bunch of cards then putting all your binned lands onto the battlefield sounds great for both ramp and landfall