For information about speedrunning Ikari Warriors and to get a better understanding of what's going on in this run, go to the guide in the SDA knowledge base (referred to as sdakb in my comments below):
After having completed my first speedrun of this game, I eventually decided to make a TAS. During the discussion in the tasvideos forum, jigwally/dugongue suggested that the flying glitch combined with death abuse could be used to save time.
When leaving the helicopter and entering the flying state, you can no longer interact with the outside environment (collect items, kill or be killed by enemies etc). This prevents you from advancing past the ends of area 3 and 4, which require killing a boss. However, if the helicopter is destroyed while in the flying state, a death is buffered and it triggers as soon as you stop flying. When you respawn, you're no longer in the glitched state and can again interact with the environment. Funnily enough, I had known for a long time that destroying the helicopter would break the glitched state, but in my efforts to complete the game deathless, it never occurred to me that this could be abused until it was spelled out to me.
Anyway, it turns out that it doesn't save time in a TAS (the death animations cost more time than what's gained back). However, it does change a real-time speedrun in some significant ways. The helicopter sections in area 3 and 4 both normally require a fuel drop. While the chance of getting these fuel drops can be manipulated to some extent, they're still major roadblocks because of how late in the game they occur. By exploiting the flying state/death abuse combination, the fuel drops are no longer needed and both of these random spots are therefore completely eliminated. With these bottlenecks out of the way, I decided to add some faster and riskier routes elsewhere in the game instead. They're not new strats and could just as well be used in a no-death run. However, they were simply excluded from my no-death run to allow for more attempts reaching the fuel drop locations. As a result, this new run ended up having quite a number of different route choices compared with the no-death run.
I'll comment here on noteworthy things, but also make some comparisons with the no-deaths run for reference. If something in my comments appear to lack an explanation, chances are that it's described in the guide in the sdakb linked above.
When making attempts, the only time losses I accepted were due to RNG. Any execution mistakes led to immediate reset. As a result, all my completed area 1 were within roughly half a second.
- 7:43 - My focus was on avoiding the several shooting blue soldiers on the bridge, instead of correctly executing the double-hit of the two helicopters with the grenade. As a consequence, I had to toss a second grenade for the second heli and lost 1.5 seconds. If there are shooting blue soldiers on the bridge, they'll usually tag me or run into me, so it was a bit of a surprise that I made it through. Still annoyed by the time loss.
- 9:54 - I took a more direct route than in my no-death run for a roughly 1.5 second save. This route is a bit riskier as it requires two "half-diagonal" shots though.
- 10:50 - Very slight route change for no additional risk. By doing less diagonal walking, I saved 0.2 seconds compared to the no-death run. This was something I found after the no-death run was completed.
- 13:11 - Not sure what happened here. I made the diagonal shot far too late. I very rarely mess up this part. I managed to wing it without any time loss, but the situation was unintentional and looks awkward for me when watching this part again.
- 13:40 - I added a riskier strat here compared to the no-death run. By doing a half-diagonal shot, you can get through the section without stopping, which saves a little under one second. This definitely adds risk though as both the timing and getting a half-diagonal shot have somewhat small time windows.
Overall, a good area 2, but the time loss on the bridge at the beginning prevented it from being great.
- 14:06 - I overshot the diagonal walking and got slightly out of position. Only a small time loss, but that was sloppy (I rarely miss there).
- 14:21 - By skipping the tank and taking the left path through the water section, I saved 4 seconds compared to the no-death run. I've lost many attempts from skipping the tank, so this decision added quite a lot of risk to the run.
- 15:49 - I took a more direct route than in my no-death run for a time save of a little over 3 seconds. It's easy to get completely stuck on the green pipe at 15:53. However, I eventually found that wiggling on the controller (diagonal-up-diagonal-up-...) seemed to work most of the time. With this route, you're left a bit more exposed when dealing with the rail gun after gate, but overall this route turned out more consistent than I first had thought.
- 17:14 - Jerk spawn... I've had this blue soldier appear several times in the past, but it's uncommon. You'll be tagged for sure if you ignore him and try to run past without stopping. I lost a little over half a second.
- 17:20 - By launching a missile just before entering the flying state, the helicopter explodes, which will buffer a death for when the flying state is left. The overall time save is around 5 seconds from a more direct to the helicopter (not requiring setting up the fuel drop manipulation), no diagonal movement in the flying state compared to the helicopter and from the resulting different approach on the boss.
- 20:17 - A bit of bad luck with the location of the stairs for a time loss of around 1.5 seconds compared to the best stair location (on the right side).
There are more minor things to comment on in area 3 such as bad positioning etc, but overall a decent area. A better stair location prevented it from being good.
- 20:47 - For some reason I thought the rail gun spawned a bit late. When that happens, its explosion can hit you and it can also fire the missile horizontally instead of diagonally. The mitigation when that happens is to move a bit diagonally right (for the explosion) and add a small pause (for the horizontal missile). Unfortunately, I can now see that my assumptions were wrong. I could have safely walked in a straight line without stopping. The time loss should be something like a bit over half a second. It breaks the flow in a pretty cool looking section though, so I have some regrets over this decision.
- 20:50 - Right after the poor decision above, I overshot the diagonal walking and ended up on the slope. A little under half a second lost, but it hurts a bit watching it since it was really unprovoqued.
- 21:13 - Around 8.5 seconds saved over the no-death run by skipping the tank. Needless to say, being exposed on foot for such a long section comes with a significant risk increase.
- 21:52 - Super close call...
- 22:12 - Since I don't have to manipulate the fuel drop in the heli section, I can take a more direct route and skip time consuming manoeuvers connected to the fuel drop manipulation. Around 10 seconds saved.
- 23:06 - Around 11 seconds gained by traveling in a straight line compared to the no-death run, but also by not having to collect the extra fuel.
- 26:30 - Leaving the flying state and triggering the death at this point is a guarantee for making the "teleportation jump" forward to work. On emulator, I have through various testing managed to do this around 1.5 seconds earlier. However, triggering the jump earlier is very unreliable and I have not found any good pattern for this. Leaving the flying state too early is a really bad idea. The jump forward will not scroll the screen enough (or not at all). This means you'll respawn further from the boss, which will cost several seconds. On top of that, the last enemies might not walk off screen, which is basically a run ender since they are programmed to home in on you. In short, without having a reliable way to know how to set up for an earlier jump, the time loss felt from playing it safe felt justified.
- 26:50 - Unfortunately the boss didn't die from the 10th grenade and I needed one more grenade (1.5 seconds lost). I know this is more likely to happen with the default grenades, but I don't know the reason for it or if it's possible to control.
The start was pretty shaky and the end was unfortunate. Other than that, a pretty good stage.
I must admit that this speedrun was more something that I felt had to be done than something that I was really looking forward to. I definitely think it was worth it though. This run turned out to be almost one minute faster than my no-death run. Much of it comes from just being able to use riskier routes. Looking at the final result, I'm glad that the new run ended up being quite different from the no-death. Even though this game will for obvious reasons never be a popular speedgame, I believe the addition of death abuse has made it a lot more accessible, which I also think is a nice bonus.
By no means do I claim this run to be at the limit of what's possible, but at least there is now a good demonstration of the route. I hope the run will be entertaining to a few people and possibly also help the next person interested in speedrunning this game off to a good start.
Thanks to jigwally/dugongue for spelling out for me how deaths could be used to save time in this game.