I found about a 20 frame improvement for Level 12 today, with Gate Thief #1. The result brings the displayed clear time down to 0:29 on the game clock. I'm going to try to record a better video of it today.
Anyway, here's the hybrid best times board I promised. This picture includes the best possible displayed time for every level. After acquiring Gate Thief #1, and doing all of his best records, I reset the console, which clears the sprite corruption while preserving the current records on the board. Then I acquired Gate Thief #2, which does not cause any garbage or overwriting to occur on the best times board. Then I did GT#2's best levels (Levels 4, 8, and 11). I found it more convenient today to get the "0:22" on Level 1 with the normal Prince Sprite, although GT1 & GT2 are both perfectly capable of matching it.
I take great pleasure in knowing I'm the first person who's ever seen these particular numbers on this screen. Now you all can join me in enjoying this pretty picture!
Of course, these records are all confined to the rules of only using warp glitches, but not Game Genie Codes or Debug Code. Interestingly, there is a Game Genie Code for "No Gates." It does not help you climb through a gate from below, but it does let you run or jump through any gate at the same ground level as the prince, without any consideration for timing or spacing. It is an interesting exercise for the mind for me to imagine where an improvement might be made to the displayed game clock per level, if someone were to use the Game Genie Code instead of a Gate Thief.
Level 4 would definitely see a huge improvement, by being able to jump through the gate above the entrance room.
Levels 6, 7, and 9 might each allow for a 1 second improvement, but maybe not.
I can imagine level 11 might allow for 1 or 2 seconds, if there was a way to go through the first two gates while avoiding all of the spikes, for a quick turn-around from the upper hallway. I might be interested in exploring this.
Level 13 could definitely see some improvement. Given Gate Thief #1's unique skill set, he destroys all other versions of the Prince on Level 13, but there are also some limitations, most notably the two gates leading into Jaffar's Cage, and the gate leading to the conveyor belts. Definitely several seconds could be saved on this level.
Level 16 could see a small improvement at the gate before the Boss, but it's hard to say if it would be enough to save 1 second.
Level 18 could see a very small improvement, but not enough to save 1 second.
Level 19 could see a big improvement at the final gate, after the fight. This would essentially combine the skill sets of GT1 and the Fat Gate Thief, and may save 2 seconds. The difference between GT1 & Fate Gate Thief is 118 frames in the room after the fight, which is 2 full seconds on the game clock.
To summarize, Levels 4 and 13 would see giant improvements in displayed clock time with the Game Genie Code for "No Gates." Level 19 would see a 2 second improvement, and Level 11 might also see an improvement. Levels 6,7,9,16 might each give up a second. But I think the other levels will not give up any additional time by expanding the Prince's flexibility with gates.
I may be able to test my theory of level 16 directly, by using the Fat Gate Thief. I think he would be completely unencumbered by gates on this level, but I have never tried, since his relevance has been limited to the "Sub-9" speedrun, which begins with the Level 16 Checkpoint Warp. I haven't really bothered to test his full capabilities on Level 16 from the beginning of the level.
Edit: Fat Gate Thief can have a theoretically perfect gate setup on level 16 (comparable to Game Genie Code), for a 40 frame improvement, which is 5 time units. Unfortunately, Gate Thief #1 just crossed the threshold for 1:04, so 7 time units would be required to achieve 1:03, and that's not going to happen. So the Level 16 record is safe.
Edit: Fat Gate Thief can demonstrate the basic idea for Game Genie Code route on Level 11, via the upper hall, and save more than 1 second relative to the best GT routes. It would appear that given how close Gate Thief #2 is to 1:10, GGC will be able to produce 1:09. Very doubtful that another second could be saved on top of that, since there are no codes to avoid spikes and fire. However, there is another Game Genie Code which allows for infinite fall distance. Whereas invincibility mode requires landing near a wall to pop up, the GGC will allow you to land anywhere. So that code could be used to fall all the way down the pit, in the room before the chomper & gate. I may be able to sketch out a rough idea of that timing via emulator; I do not have a Game Genie for my console, where I do my official testing. Suffice it to say, Game Genie falling code could be used for a great improvement on level 11.
Edit: Fat Gate Thief (non-invincibility) is actually 1 time unit faster than GT2 on Level 4 INV. I'm not sure if it's good enough to change the clock. Time to make another video!
Invincibility:
The optimal route for "all 20 levels" speedrun would create a slightly different Best Times board. Level 1 will display "0:23," because it will be identical to the TAS route, prior to unlocking Gate Thief & Kill Button. Levels 3 & 14 will reflect the non-invincibility times, shown above. And Level 20 will show "0:01," because too much time is wasted by repositioning the Prince to achieve the "0:00" time on the board.
I realized I had what I needed to repeat the Inverted Intro, with the simple change of making sure Jaffar is dead. That would reset to the Logo, instead of just resetting to Main Menu. So I repeated the non-sense I'd been doing, and it worked like a charm!!
I did it a few more times to make sure, and then recorded this video. I've cut the full setup off for now, so everyone can have a quick, convenient video of just the "Inverted Intro." I'll upload the full setup shortly afterward, so everyone can do it themselves and impress their friends!
Link to video