As in Fig. 14, showing the same five quantities and tracking the same cluster from TNG300 through time but here focusing on high redshift, i.e., showing details of the first two transformations to higher core entropy. These occur at z ≃ 1.2 and z ≃ 0.95, and are marked with the vertical dotted black lines. The merger at t_lb ≃ 8.5 Gyr causes strong bulk motions in the inner ICM, enhancing the episodic AGN accretion and feedback, which collectively transform and remove cool gas from the cluster core.