Why is Magnus coming to help? Again, I got to ask: Why can’t they just steal a boat? Jace says wards protect the boat, but as I pointed out earlier this week that Jace seems to get on the boat just fine without encountering the wards. Yet, all of sudden they need Magnus for the wards?
Yes, the demons guarding the boat is a problem. But I don’t see what Magnus can do it about the situation. He is a part demon himself, and a lot of the demons on the ships are Greater demons.
So Magnus could also be outmatched on a power level (because of even the Warlock, in the beginning, had trouble controlling Agramon but outnumbered as well). He’s only one Warlock against a possibly legion of Demons.
No, what Jace should have done was take Luke and the Lightwood children with them.