It's not necessary (or, in some cases, possible) to identify which roll was the third
Human decks tend to spread counters through all of your creatures, allowing Esper Sentinel to grow to levels where paying to stop its effect proves impossible
three mana is cheap enough that you'll have most of your hand to follow it up with
Sure, she's pricey at six mana, but three colors that all love artifact, and then has a sizable body with flying to swing in the red zone and has an immediate impact on the battlefield
Im not entirely convinced that a 1/1 has all that much impact, but it can do a job against decks without Day of Black Sun
Kirri, Talented Sprout A programming note: While many cards have received an errata that replaces postcombat main phase with second main phase, Kirri, Talented Sprout has received one that states each of your postcombat main phases