z = 0 cluster mass function of the new TNG-Cluster simulation project (blue) stacked on top of our existing cluster sample from TNG300 (orange), showing the number of halos per 0.1 dex bin in M_200c. We increase the statistics for halos ≳10^14.5 M_⊙ by an order of magnitude, from ∼30 objects to ∼350. Likewise, we increase the sampling of the most massive and rare ≳10¹⁵ M_⊙ halos by a factor of 30, from just three halos in TNG300 to ninety in TNG-Cluster. The combined M_200c > 10¹⁴ M_⊙ cluster sample increases from 280 to 636 halos.