Alright, here is a trick that I feel should be documented for posterity. However, it unfortunately turned out incompatible with any fast approach for doing this section.
The Fast Grant Orb drop
Rarely, the boss orb on defeating Grant will fall one pixel further to the left, causing it to land on the raised ledge. This allows Trevor to pick it up earlier, saving a few frames.
The reason it works is because some properties from the enemy that previously occupied the orb's object slot were not properly cleared. Specifically, the orb shares some properties with this Medusa Head in the previous room:
More generally, every second medusa head that spawns will always occupy the same slot as the orb.
The way it works is that, on the first frame spawning, the game sets the orb's X speed to 128 subpx/frame. The orb inherits the X subpixel position (0x50B) from the Medsua head, so if it above 128, it will roll over a full pixel. However, if bit 3 (0x8) of the orb's status byte (0x560) is set, the game considers it facing left, and will move it left. Now, with a sufficiently small subpixel position, it will roll over one pixel to the left, which is how it lands on the upper ledge.
Before the orb, the status byte is used by the Medusa head as a hitstun timer: On taking a nonlethal hit, it will be set to 16 and count down to 0.
The status byte is also used by Grant himself, who will set it to a specific value when performing certain projectile attacks. In particular, throwing an axe or a dagger to the left left will set bit 3, and him throwing one to the right will clear it.
So, the steps to reproduce it are as follows:
1.Injure the Medusa Head with a nonlethal hit and kill it within 8 frames to prevent its hitstun timer from dropping below 8. This sets 0x560 to the right value.
2.Prevent further Medusa Heads from spawning and overriding 0x560
3.Make sure to leave the vertical room with $50B set to 127 or less
4.Prevent Grant from launching any projectile attacks to the right (to the left is OK)
5.Presto, fast orb drop.
So, why is it not helpful?
In the clip you see, Trevor can collect the orb earlier, and also much further to the left than before. This finishes the stage faster, however, the subsequent cutscene will take longer, because Trevor will start further to the left and take more frames to walk to his destination in the cutscene. This more than cancels out the frame savings from the orb drop. It might potentially be ameliorated by Trevor being as far right as possible while collecting the orb. However, I've not been able to find a strat that kills Grant fast enough and still gets Trevor in the right position to collect the orb in time. Because of this, I decided to share the explanation here, in case it might be made useful in the future.
So yeah.
