They spent a few moments to seal off the entrance and then they had free rein in a field containing 75,000 lambs ready to be sacrificed. It was perfection.
The Dark Lord wanted them to blend in to create more chaos. Trousers and a shirt replaces the robe, but his wand was still there. He cast the first spell, cutting a man's face, watching the blood ooze out. It wasn't fatal, but it attracted everyone's attention, and then the Imperius, the man telling everyone that a City fan had thrown a glass bottle at him. No one thought about the fact that the bottles were banned or that there were no glass shards on the floor. No, they started to push breaking the glass that separated the two groups of fans, and then chaos broke out.
Once his job was done, he began Apparating in different areas repeating the process. Only when there were enough riots, did he begin to enjoy himself, hurting and killing at random.