Navigator's Ruin

Enchantment

Raid — At the beginning of your end step, if you attacked this turn, target opponent mills four cards.

2018-01-19:
Raid abilities care only that you attacked with a creature. It doesn’t matter how many creatures you attacked with, or which opponent or planeswalker controlled by an opponent those creatures attacked.
2018-01-19:
Raid abilities evaluate the entire turn to see if you attacked with a creature. That creature doesn’t have to still be on the battlefield. Similarly, the player or planeswalker it attacked doesn’t have to still be in the game or on the battlefield, respectively.
2018-01-19:
Some raid abilities trigger at the beginning of your end step. These abilities trigger if you attacked with a creature that turn, even if the card with that raid ability wasn’t on the battlefield when you attacked.