Heh... I remember playing Free Play on the city mode with my friends, and since we just used Action Replay to skip all the challenges crap, we had Hydra unlocked. Predictably, everyone chose it. In a matter of seconds, the three other Hydras were destroyed by each other. From then on, it was a neverending battle to take the single Hydra down... though half of my time one person was just cruising around with the Dragoon, minding his own business. Once finally I got the Hydra, I stuck around on the top chandelier-ish platform, waiting for the prey to come to me... sure enough, they did. Three vehicles in the air surrounded me, and every time they landed on the platform, the three-second battle ended with me as the victor. Ah, good times....
Shame it felt like it didn't have much replay value when playing by myself. Then again, I DID use Action Replay to clear all the challenges....