The Titan was a "world event" as was shown in the top right of the HUD. Meaning it was a random open world event that popped while they were going further towards the area where the mission was set.Obviously your buying into this. But i need more then just game-play, which looks pretty basic as i said. You shoot missiles, fly and shoot big monsters that apparently let you pass them with much counter-interaction(odd moment).
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They didn't have to engage with it, it was a bonus and the monster couldn't stop them from just flying into the water.