God of War: Ascension's fourth multipalyer mode is Trial of the Gods, a two-player co-op (or solo) mode where you have to face five increasingly difficult waves of enemies. The twist here is that you're racing against the clock while fighting the monsters.
Every beast you kill adds time to your clock, and you'll get bonus time depending on how fast you defeated a wave. Once all five waves are cleared, you'll have to face off against some kind of boss. Any experience gained in Trial of the Gods mode will also go towards upgrading your character in the multiplayer versus modes.
God of War: Ascension: Trial of the Gods Revealed [PlayStation.Blog]