Wave 2: Rise of the Combiners
No. you count the number of characters in your opponent’s KO area when the ability resolves. After that, even if you KO another character, the attack bonus won’t change.
If you attack with Dirge and it does more than enough attack damage to KO the defender, Steamroll’s ability will work, but Dirge’s ability won’t trigger. If Dirge does exactly enough damage to KO the defender, Steamroll won’t do anything.
Autobots have a red frame and the Autobot insignia in the lower right corner. Decepticons have a purple frame and the Decepticon insignia in the lower right corner. A few characters have "Autobot" or "Decepticon" in their names, although these aren’t the only Autobots and Decepticons.