Beanstalk Control is loaded with artifact mana and value engines (Lotus Petal, Giant's Boulder, The One Ring, Expedition Map), making Null Rod a huge blowout that shuts down those pieces. It does nothing against Karn or Trinisphere, since Karn is a planeswalker and Trinisphere has no activated ability. Our Chalice of the Void is less appealing here since their Trinisphere already punishes cheap spells and they can sculpt around a single Chalice count with varied curve, plus Chalice would hit our own Lotus Petals; trimming it for more proactive artifact hate is better. The extra Eldrazi Confluence adds another flexible instant. It can exile and return a Trinisphere tapped, so it stops taxing spells until it untaps. It can also make Eldrazi Scion tokens that can attack Karn or Ugin. Sire of Seven Deaths is the clunkiest top end here, and Kozilek's Command and Giant's Boulder give them ways to answer it, so one copy makes way for the extra Confluence.