Fire Navy Trebuchet's controller chooses which player, planeswalker, or battle the token is attacking. It doesn't need to be the same player, planeswalker, or battle as other creatures are attacking.
Defender, reach
Whenever you attack, create a 2/1 colorless Construct artifact creature token with flying named Ballistic Boulder that's tapped and attacking. Sacrifice that token at the beginning of the next end step.
