Colossal Boy is pretty tough, but he’s nowhere near Supergirl level. Her speed is much better than is and so is her power. Heat Vision can’t hurt and she’s also a better hand to hand fighter. Colossal Boy may have been doomed from the start, but at least he tried right? Maybe next time he’ll get to pwn. Supergirl wins.
Even when he grows to a giant size, he still can’t beat Supergirl who’s smaller in size than him and she totally overpowers him and completely destroyed him. Imagine if their sizes were swapped, and it’s Supergirl who grows giant instead and Colossal Boy is stuck at regular human size. A giant Supergirl vs regular human size Colossal Boy. It would be an overkill. Giant Supergirl would just be to overpowered for regular human size Colossal Boy.
Yeah that would definitely be crazy. Supergirl definitely has the edge in either scenario but if she were huge that would be pretty crazy