I don’t know if this is a mistake or what, but Amazon is giving Twitch Prime members a $15 credit with purchase of select games. Two of the games are on sale for $15 for Prime members right now (Fallout 76 and The Last of Us Remastered), making them essentially free. Another one (Gears of War 4) is on sale for $10, which ends up putting you $5 ahead once the credit arrives in your account.
The $15 credit will arrive in your account 7 days after the purchase goes through. You can read more of the small print on the deal’s page.