Mystical Dispute is fully cascade-safe at 3 mana value and directly answers their blue spells (Subtlety, Waker of Waves) while also functioning as a counter against Living End itself for {2}{U} unless they pay {3}. Force of Negation can counter noncreature spells such as the sorcery Living End (cast via cascade), but since their creature-type cyclers bypass it, it comes out; we keep Force of Negation's namesake logic in mind but this is the one clean cut. We are not touching Narset, Teferi, or our sweepers, since Teferi's static ability and our removal remain excellent at unwinding their graveyard plan and answering the post-Living-End board.