Don't lie: when you first met Mars Bar, didn't you think he was going be the bad guy? He's got all the right attributes: a huge ego, can be a little mean, seems to hate our hero. They even go head to head in their very first meeting: "Maniac blinked and stepped back. The kid stepped forward. They traveled practically half a block that waySo, where does the "good" part come in? It takes a while, but eventually Mars shows his softer side. That's not too surprising. What is surprising is that this good side only appears after Maniac drags him into the McNab house for maybe the worst birthday party ever.
We don't exactly know why, but it probably has something to do with Mars figuring out that Maniac is like the other white kids. He's brave and kind, and so he and Mars find common ground out in the early-morning streets. They stop racing each other and end up running alongside each other instead:
Morning after morning it happened this way—the two of them dovetailing at an intersection, and, without the slightest hitch in stride, cruising off together. Though each face showed no awareness of the other, they were in fact minutely sensitive to each other.
This is just what Maniac needs: someone to run with him and to make sure he's not alone. And this is also what Mars needs: someone who challenges him, someone he knows he can't beat with some trash talk and just a little effort. It's even better that he and Maniac don't love each other from the get go: they earn their friendship.
