Kill at least 10 enemy troops from a rolling cannonballThere are a couple of ways of doing this. The simplest is to play a skirmish or multiplayer game against a single hard difficulty AI. Once it starts use the “speed always wins” cheat so they can amass a large army. In the meanwhile also use the “Ya gotta make do with what ya got” cheat a couple of times so you get some mediocre bombards. Once the enemy attacks with a large army, just keep attacking them with your cannons until it unlocks.