Skyscraper District and Pharaoh Park
Theorized Cop Skip
If you can somehow get to the other side of the cop trigger at the beginning of the level, you can finish the graffiti like normal and skip the cop fight. The only plausible theory we have now is to pickle in between the collisions of two of the highway walls, though this has never been successfully done. Regardless, this method would likely be much too random and difficult to be RTA viable.
Death Warp Abuse
Because this entire level is comprised of death voids, you can abuse this by strategically voiding to get to a certain spawn point faster than skating normally. This picture is a chart roughly showing where different death voids are and where they spawn. This chart is merely for reference; if you want to learn a route, it's best to just watch a video and copy the death warps as best as you can.
(picture coming soon)
Of all the death warps in Skyscraper, this most useful one is the one that spawns you right next to Sky Dinosaurian Square. There are several ways to warp there, but they all involve falling just next to the entrance to Highway Zero.
Water Tower Warp
On the far northwestern part of the map, there is a spiral grind that wraps around what could be considered a water tower. To skip this grind, a precise boost and deathwarp is used just before it, as shown in the video.
This is a clip where we get pushed into a building, which allows us to reach a valuable death warp very quickly. It's called Onion because you go through layers (of textures).
You can trick jump off of the slope of the building into the billboard collision, which will push you through the building. Then skate to the edge of the platform and jump into the warp. You must jump, simply skating off the edge won't work.
Funion, or Faster Onion, is a faster setup for Onion. You can grind and jump off of the golden pillar and fall in between the billboard and building, achieving the same result.
In the section with the M and L with the twisty red girders, one of the girders can push you through where the walls meet. This is a slightly faster way of reaching the other side, but isn't currently used in any route.
An optimal observatory climb uses two jumps in order to skip a long set of grinds.
The special challenge for this level says to grind around the Pharaoh, but this isn't entirely accurate. You don't need to grind around the Pharaoh, you just need to be grinding in the general vicinity of the Pharaoh for 30 non-consecutive seconds. It's more optimal to just grind in place until you unlock the soul, because then you can guarantee to be as close as possible to the next graffiti.
At the Observatory, the glowing blue rails on the side of the health cans have some wonky physics. If you grind backwards on it and allow yourself to fall back down into the floor, you will repeatedly fall onto the rail almost every frame. You can jump your way out once you're done with it. The left rail (when facing the rails) will cause less of a flickering effect than the right rail.
Reaching Ends of Highways/Train TracksDiscovered by S4ND1B4RT, September 2011
By boosting from high vantage points (such as the silo), there are several ways to jump over loading zones and skate to the ends of the highway and train tracks. Not really useful apart from quick travel time in certain scenarios.