DmC - skip first half of Under Siege (Mission 12)
4You can go out of bounds near the start of the level, right after collapsing the two pillars. Do a jump against the right side of the rubble dead end, so that you start the jump facing forward and end the jump facing towards right. If done correctly, Dante will start his crazy hopping motions, indicating that he is inside collision. From here you can carefully jump again and slip past the collision and go further into the rubble dead end.
Here, get to the back-left side and do jumps towards the corner and the left wall. It isn't too hard to slip through the wall here as well, and now you're officially OoB. There should be a strange candy-cane coloured block left by the devs near you. You can use that to climb on top of the rooftops.
From there, you can basically jump through the entire first half of the level... except that if you go too far ahead, you'll get stuck since there's a locked door and you can't get it open since Kat is nowhere to be seen. So instead activate the cutscene of people getting shot from outside bounds and from there on you can complete the level like normal.
Should be a pretty big time save in a speedrun since this is normally one of the slowest levels in the game. I think you could cultivate the route further by being more fancy on the roof, by jumping over some more chasms for example. I didn't want to do it because I was sick of falling down so many times already, and just wanted to show you this basic speed route.
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DmC Glitch FAQ:
http://www.gamefaqs.com/ps3/605600-dmc-devil-may-cry/faqs/68707