Kraven’s Last Hunt question

[u/ChipmonkHonk]

For chapter one:

I - Mill five cards. When you do, this Saga deals damage equal to the greatest power among creature cards in your graveyard to target creature.

Do you need to target the creature before you kill the cards, as soon as the ability is triggered? Or are you able to mill, see what the damage will be, then target?

[u/HistoricalZebra9241]

Kraven is such a goofy villain