We eventually need a marksman whose basic attack hits in a perpendicular line, like a Colossus

Twitch can attack in a line with his ultimate, but so far we don't have a Champion whose attacks can hit in a perpendicular line. That could be pretty useful in some niche situations.

If you need an example of how this works, look no further than the Protoss Colossus. Man, I love those things. You guys probably hate them, but there's nothing quite like using a group of Colossi to roast an enemy Marine/Marauder army.

And if this is too broken to be a passive, then it could be an active limited-duration effect like Spray and Pray.