Eldrazi runs its own set of 4 Chalice of the Void and big colorless threats like Reality Smasher and Thought-Knot Seer, so we want cheap interaction aimed at their colorless spells. Disruptor Flute works best by naming a specific key spell such as Thought-Knot Seer or Reality Smasher, which then costs 3 more to cast, or by naming Eye of Ugin to shut off its search ability. Naming a land only stops its non-mana activated abilities and does not tax their mana or their colorless spells in general. Consign to Memory comes in because nearly all of their spells are colorless, including Eldrazi Linebreaker (devoid), Kozilek's Command, Eldrazi Confluence and their Chalice, and it can also counter triggered abilities like Thought-Knot Seer's enters trigger. Keep in mind that Cavern of Souls makes creature spells of the chosen type uncounterable, so Consign is better against noncreature spells and triggers when they have it. Thoughtcast costs {4}{U}, so it has mana value 5. Only a Chalice set to 5 would counter it, which is unlikely, but it is a slow card-draw spell against a fast deck, so we trim it. Our own Chalice of the Void stays in, since set to 2 it can counter their It That Heralds the End and Wastescape Battlemage while barely touching our own spells.