War-Name Aspirant
Creature — Human Warrior
Raid — This creature enters with a +1/+1 counter on it if you attacked this turn.
This creature can't be blocked by creatures with power 1 or less.
No battle means more to a Mardu warrior than the one that earns her war name.
Illustrated by
Khans of Tarkir#126UncommonEnglishLegality
Rulings
Once a creature legally blocks War-Name Aspirant, changing that creature's power to 1 or less won't change or undo that block.
Raid abilities care only that you attacked with a creature. It doesn't matter how many creatures you attacked with or which player, planeswalker, or battle those creatures attacked.
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, planeswalker, or battle it attacked doesn't have to still be in the game or on the battlefield.