Pick a boss and your build and the simulator answers: how many nail hits, how many spells, how many of its hits you can take. There are 180 entries, every boss and the Journal's enemies, with their health, their phases and each attack's damage.
You can fight hit by hit: the soul you gain, the masks you lose, stagger, the charms that act in combat (Dreamshield, Weaversong, Grimmchild…) and undo when you get it wrong.
1500 in the main game, 1250 on Attuned and 1650 on Ascended: 72 hits with the Pure Nail.