Takedown Events are a mode where you have to destroy as many Crash Karts as possible, the more you destroy, the more score you get, which will be required for getting 3 stars. Just play a lot of Takedown matches and you should get this over time, no need to find to think off a certain character or track to cheese this on, i recommend playing Takedown in every track for the sake of variety, so it doesn't get too boring, which you will probably will have to do so anyway if you're going for all the stars, if not, then just play a lot of Takedown Matches until you get the achievement.