Sultai Aluren is a combo deck assembling Aluren plus creatures or Show and Tell into Omniscience/Atraxa, so proactive disruption and mana acceleration matter more than reactive countermagic you may not have up. Carpet of Flowers punishes their heavy Island count and accelerates you into Leyline Binding or Up the Beanstalk plays ahead of schedule. Lavinia, Azorius Renegade shuts off Aluren's casting loop and Omniscience by countering any spell an opponent casts if no mana was spent to cast it. Force of Will remains the priority countermagic; Force of Negation and Spell Pierce are cut since this matchup is often decided by tempo and racing rather than fighting over the stack turn by turn.