Ikari_Warriors_(NES)

Level by level description

Level 1

Foot1 to tank - https://www.youtube.com/watch?v=ng2d8bxsp-Y
If you start speedrunning this game, you'll see this section many times. This is where it becomes apparent that the game's rng must be fairly primitive. The enemy movements are clearly intended to be random, but you'll soon be able to correctly predict many of the movements. There are still far too many possibilities to be listed here.

Tank to foot2 - https://www.youtube.com/watch?v=xtsxcUEJTgc
All the upgrades (F, S and L) are absolute requirements for the route to work. The first part is plagued by random grenade thrower spawns. They should only occasionally be able to hit you, but they're still an annoyance.
It's very feasible to get through the first section without having to turn the tank cannon to save a few frames. It exposes you more to the grenade tossers and you have to adjust slightly when taking out the first tank though.
The rest of the section is mainly to hope for not late tank spawns because of the sprite limit and getting the timing down to take out the gate guards without touching the gates. One enemy that frequently creates problems is the tank on the bridge after the first gate. Normally, you can just go straight forward, fire off a tank shell, which will hit it. However, if there are three soldiers or more on the screen, the tank won't spawn and the explosion from your shell will disappear before the tank spawns. An easy fix is to just wait for it to spawn, but this can incur a one to two second loss. A faster alternative is to move out to the right side and take it out with a diagonal shot, but you're then also exposed to the tank's shots if it spawns earlier than you predicted (since the enemy soldiers are spawning randomly, you can't be 100% certain in each situation if the tank will spawn late or not).
On the last stretch, blue soldiers frequently spawn on the left side. If they don't run into the tank, they will home in on you and catch up to you once you leave the tank. They can easily be taken care of though by either making a quick halt and let them run into the tank or change the cannon direction and shoot them diagonally. Both of these options incur minor time losses.

Foot2 to helicopter - https://www.youtube.com/watch?v=o7IWBK-6ASg
There are four or five enemies you need to care about here. The optional one (not shown in this video) is a blue spawn that will come at you when leaving the tank. This soldier has to be shot down. Sometimes he comes at a bad angle and you need to adjust (for a small time loss) in order not to run into him. The other four can easily be taken care of with grenades as shown here. The first one is a machine gunner that will also home in on you. The next two are self-exploding guys and the last is the rapid machine gunner right before the helicopter. Maybe 5-10% of the time, the mine will kill you if you walk in a straight line. If you want to reduce that risk (at the cost of a few frames) you can slightly tilt to the left when you're walking alongside it.

Helicopter/flying glitch to the end - https://www.youtube.com/watch?v=7mnjs6Px1hM
The flying glitch is described in the Game Mechanics section. Normally when you leave the flying state, you get teleported forward or backward a little bit. This all depends on where/when you left the helicopter and when you left the flying state. If you set it up so that you teleport forward and then start walking, you'll always get a small teleportation backwards after a second or two. This backwards teleportation is non-desirable. By flying out to the left side as shown in this video and leaving the flying state at the right moment (if you fly further, you'll hit an invisible wall that you can't fly through), you can hit the end of level trigger before being teleported backwards. It's unknown why you have to fly out to the left for this to work.

Level 2

Foot1 to foot2 - https://www.youtube.com/watch?v=oZLq2LSZoI8
This part of the game is tricky even with all the upgrades because of many possibilities for random spawns. Starting without upgrades (because of not collecting the heart in level 1 and flying over some of the important items) makes it even harder. The key areas where survival will have to take priority over speed is from the open area where the SS is found (this place can be crawling with shooting blue soldiers) until the first water section. But random spawns can pop out of no where in several other places as well and cause trouble.
- Any blue soldiers that come close to the right side around the SS item will likely be a considerable threat. Many of the movement patterns of these soldiers will bring them in your way (including firing your way), so it's recommended to stop and take them out, even if it means a time loss.
- If the big tank doesn't shoot a grenade as you approach (rng), you can clear the bridge area ~40 frames faster, https://www.youtube.com/watch?v=NWnPupDT-gY. The risk of bad enemy patterns appears to be higher with this route.
- It's possible to manipulate the tank into firing diagonally into the water instead of on the bridge. You need to pause briefly between the bridges and there is only a 3-frame window for this to work. Overall, this approach would be a second faster or so since you don't have to wait for the explosion of the shell on the bridge.
- There are three guaranteed spawns at the beach. The pink soldier (harmless), a self-exploding guy (taken care of by the grenade) and another blue soldier. The latter will surface and hit you if you don't take it out with the gun as soon as it appears on screen. The problem in this area is instead the random blue soldiers. They both like to run into you and shoot you. There is no real guideline for how to deal with them. The firing and movement patterns in this video have been developed to take out many of the possible spawns, but are far from guaranteed to work in all cases.
- There is a knife on the left side of the first beach (see Level Maps). It would make the rest of the section easier, but is a bit out of the way and would cost 3 seconds.
- The remaining parts are also very luck-based. There are several possibilities for random spawns that will end up firing at you. When possible, it's worth to go a little out of the way to take out potential threats. No matter what, the success rate will be very low (~10%?) of this whole section (end of the video).
- Entering one of the tanks around the stone faces will end up costing ~15 seconds compared to getting through the section on foot. One reason is that the tank will have to take a detour around the white structure because of the marshes.
- There are many dangerous possibilities for spawns on the other side of the white gate. Depending on where you pass through the gate (horizontally) you can avoid some of these difficulties (but also adding others). The path shown here (pass through on the left side, but still enough to the right to trigger the self-exploding mechanism of the gate) works fairly well (at least better than the alternatives). Still, this area is risky.
- There are many grenades that are tossed that appear to be a bit random in this video. They are based on anticipating possible enemy spawns that can cause trouble. These mitigations are however no where near covering all possible enemy patterns.

Foot2 to foot3 - https://www.youtube.com/watch?v=tyBhJRYkRR8
This part is split from the previous in order to show it on foot as well as in the tank. Even though there are quite a few random shooting guys along the way, they tend to (a bit surprisingly) not be bothering you too much as long as you follow the path shown here. There is nothing tricky about the execution and it's not that much more risky to take section on foot than in the tank (obviously a bit more risky though).
While it's not that hard of a section on foot, it's of course still more risky than in the tank. For the sake of completeness, here is the section in the tank, https://www.youtube.com/watch?v=2EIX8pgjl-I. With one exception, this section in the tank is almost a formality. The tricky part is around the gate. There is a missile target plate that is very inconveniently placed and that creates a non-neglible risk of taking an unavoidable hit (a risk that is not present when on foot). This section is ~12 seconds slower in the tank than on foot. Roughly half of that comes from the fortress (it would have been more if the part after the fortress didn't require you to stop so frequently when on foot).

Foot3 to the end - https://www.youtube.com/watch?v=uwsvacbPVy4
- At 0:59, you can also take to the right. If there are no enemies (rare), it's ~half a second faster to go straight. If there are enemies, straight and right are time-wise the same, but it's usually a little more risky to go straight. If you go right, you won't get the heart here, but it can be collected without time loss right before the end of the stage instead. It boils down to preference which path to choose.
- At 1:09, you have again two paths to choose from. Left is shown here, but it's time-wise the same (or at least very close) as going to the right. There doesn't appear to be a big difference in risk either (but right has been significantly less investigated).
- If you're too fast past the first tank in the pink structure, it might fire a second missile horizontally instead of diagonally down. This is easily prevented by introducing a momentary pause after tossing the grenade.
- The last enemy in the pink fortress is shot by a 'half-diagonal' shot. This shot is explained in the game mechanics.
- There is a slightly faster (and riskier) path through the first part of the pink fortress: https://www.youtube.com/watch?v=SeBvXYMcNhs. It saves a second (but also has a downside of 2-3 seconds if not successful).

Level 3

Foot1 to tank1 - https://www.youtube.com/watch?v=-eGQLme7jFM
Easy. The only part where you have to be a bit careful is to not miss the shot at the grenade thrower.

Tank1 to foot2 - https://www.youtube.com/watch?v=vjMInsi2xP8
Again easy. If you get soldiers on foot behind your tank, it's quite likely that they will shoot you in the back once you have left the tank. If that happens, you will more or less be required to stop and get them in front of you or reverse to take them out.
Doing this on foot would turn this easy section into a very luck-based part and the time gain would be quite small (a second or two). For illustration, it's shown here: https://www.youtube.com/watch?v=hbRetegUhsw

Foot2 to foot3 - https://www.youtube.com/watch?v=OqLcqGLWwZ0
The end of the water section is quite often plagued by random bullet-shooting soldiers, but it's overall not too bad. It's worth pointing out that by walking over the corners in the water section, you save a little time compared to walking around them.

Foot3 to helicopter - https://www.youtube.com/watch?v=z1zxuo6ALFQ
Mostly predictable, but still quite long and somewhat risky because of the possibility of random shooting soldiers in a few areas.
Using the tank is of course a bit safer than continuing on foot (but actually also adds a few risks). For illustration, the tank route is shown here: https://www.youtube.com/watch?v=-iI2cIpM6yc. It's slower by over 15 seconds.

Helicopter to the end - https://www.youtube.com/watch?v=u-5QeIDSm0k
- The fuel drop is inconsistent, but seems to be roughly 1/3. It's not known (has not been properly researched) if this can somehow be manipulated.
- When exiting the helicopter, you'll be facing the direction you were last flying in. By reversing just before leaving the helicopter, you can immediately start walking down instead of having to do the half-circle turn if you had been facing up.
- The boss takes 5 hits (the hitbox is huge) and then you need to toss a grenade at the floor below the desk to reveal the exit. The location of the staircase seems to be random. It takes up two blocks and can be in one of six locations. The best you can do is to throw one grenades from the left side to cover the possibility of the stairs being on the right side. If that doesn't work, turn around and toss a grenade to the left from the opposite side of the desk to cover the remaining possibilities (as shown here). You should never need more than 2 grenades to cover all possibilities.

Level 4

Foot1 to tank - https://www.youtube.com/watch?v=rQg5hd8xGAc
The area before arriving at the pools is fairly consistent. There is always a possibility of random blue spawns that can interfere with the route though. In the pool area, make sure you toss a grenade just as you're at the corner of the first pool. Then keep holding down A (and B of course). If you walk in a straight line, you will then also toss a grenade when you're at the corner of the second pool. This will guarantee that you take out the most important enemies (including the last self-exploding guy). There can still be random enemy spawns that can kill you. If you practice this area enough, you'll start recognizing which of the random enemies that will kill you (the rng is again rather predictable, although there are many different patterns to look for). Overall, while this section looks tough, it's fairly consistent as long as you follow the path shown here and practice how to recognize dangerous spawn patterns.

Tank to foot2 - https://www.youtube.com/watch?v=3BTl35bXihc
If you carefully follow the path shown here, there should be no problems. There is only minor uncertainty with a sudden airstrike coming when going through the blue tunnels. But even then, you can recover fairly easily unless getting really unlucky with bad spawns.
This section is quite risky to do on foot, especially this late in the game. It's around 5 seconds faster than using the tank though and a suggested route foot is shown here: https://www.youtube.com/watch?v=5Ewwp2CwbIU.

Foot2 to helicopter - https://www.youtube.com/watch?v=HnI9zDMkT2w
Random enemies can appear on the left side of the water section, but are usually quite easily dealt with when it's the case. The rest is not random and quite easy to execute. The route through the barrel area can be done faster (but not by very much), but what's shown here is an example of a compromise between speed and risk. The drops contained inside the walls are determined a little before they appear on screen. For unknown reasons, the fuel drop in the helicopter area hasn't been observed by taking the right path through the water area and barrel section.

Helicopter to the end - https://www.youtube.com/watch?v=ixzhtN51Zs4
The last "missile turret" is very random and quite "intelligent" (moves in ways to avoid your shots), so care has to be taken here. The rest is fairly easy to execute. However, there is a small chance that weird things happen along the way. It can be enemies that spawn in slightly different locations and therefore being out of reach or a grenade that is tossed from one of the walls that can hit. This is rare though. The route shown here is made to be as safe as possible (it's possible to take a straighter route at the cost of some risk in some places).
The last boss normally takes 10 hits. Occasionally, the boss takes more hits. It has been observed to take 10, 11, 12, 17, 18, 19 and 20 hits. The reason for this is unknown. Fortunately, the most common is 10 (and then 17). The other ones have only been rarely encountered.