Ikari_Warriors_(NES)

Level by level description

Level 1

Foot1 to tank - https://www.youtube.com/watch?v=mfIetUyC1aQ
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 many possibilities, so they will not be listed here.

Tank to foot2 - https://www.youtube.com/watch?v=p0SzRGjiPX4
The F and L are absolute requirements for the rest. The S is a nice to have, but not at all necessary. The first part of this tank is plagued by random grenade thrower spawns. They should only occasionally be able to hit you, but they're still an annoyance.
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. An 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).
The shots during the last stretch before leaving the tank was to take all enemy soldiers approaching. If not, they will approach from behind and catch up with you while you're in the water on foot.

Foot2 to helicopter - https://www.youtube.com/watch?v=BcwUzhX_2Uo
There are only four enemies you need to care about here. They are all best 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 to the left when you're walking alongside it.

Helicopter/flying glitch to the end - https://www.youtube.com/watch?v=2tK6C_IjRTY
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 tank - [to be updated]
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) makes it much harder still.
The key areas where survival likely will have to take priority over speed is from the open area where the SS is found (this place can be crawling with semi-aggressive blue soldiers) until the first water section. Right after taking out the first pink soldier, another grenade is tossed. There is often a blue soldier spawning that will get hit by it (very annoying to deal with otherwise). The bridge with the super tank is cleared cautiously. Random spawns can make this area close to impossible with bad luck. Taking out one helicopter at a time is probably the safest way, but definitely not the fastest. Here is another video showing a faster approach: [to be updated]
This is risky though. Manipulating the super tank to fire to the side as shown here is 3-frame trick, so easy to fail. By not taking out the first helicopter, there is also a clear possibility taking a shot when it flies by. The bullets usually fly by when positioning yourself as shown here, but it's not completely consistent. Overall, this approach is ~2 seconds faster.
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 eventually shoot at you (and probably hit) if you don't take it out quickly. The best way is to just run into him after collecting the knife. 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. Try to take them out if you can and otherwise avoid them. Either way, they will frequently be faster to it than you are.
The remaining part before entering the tank is a bit easier since you're fully upgraded, but there are still several possibilities for random spawns. Especially in the area around the arrow-shooting faces (up until the white structure), the enemies tend to be quite aggressive and it's worth stopping to take them out if you can.

Tank to foot2 - https://www.youtube.com/watch?v=yuFOPXwJbbw
This part is generally easy. There are only three trouble spots. The first is that the grenade throwers on the other side of the fortress sometimes get too close to you to get a grenade in. It's rare though (~5-10%?). When that is about to happen, it might be tricky to avoid since you don't want to destroy the blinking tank (because of the resulting explosion). The second one passing the gate. It seems to happen relatively often that the airstrike hits the target plate too fast for you to get out of the way. There is no really good way to avoid this (without further investigation on how the target plates work in more detail). Trying to go through in the middle is risky because of the arrows.
It should be mentioned that it's ~1.5 seconds faster to go through the "labyrinth fortress" on foot. You can then enter the tank that is on the other side. However, that time gain can quickly be lost if you stop to take out any random spawns. Going on with the possibility of many random spawns is also risky. Entering the tank on the other side of the fortress also adds a risk because you will more often come into the range of the grenade throwers.
It's theoretically possible to run through this whole section without using the tank, but the time gained by the faster movement speed is counterbalanced by having to stop to take some of the enemies and buildings in your path. Without resorting to strats such as dodging a rain of bullets, doing this section on foot or in tank is about the same, just much easier in the tank.

Foot2 to the end - [to be updated]
You need to be very careful in the open area leading up to the "labyrinth fortress" and the fortress itself. There are many random spawn possibilities and they won't hesitate to shoot if they get the chance. Outside this area, this section is quite straight-forward as long as the execution is correct.

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=mKlgpH833vA
Again easy. 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).

Foot2 to tank 2 - https://www.youtube.com/watch?v=JdMkAsrR8xc
Mostly straight-forward. There is minor critical spot when you have to enter the water near the tank. Random spawns can appear here.

Tank2 to helicopter - https://www.youtube.com/watch?v=hL9fAFnx5II
The airstrike target plate near the beginning can sometimes give you unavoidable missiles. The rest should be consistent, but be careful to take out the critical enemies well in advance (as shown in this video). Small execution mistakes will in several places leave you open to hits that will destroy the tank. This section would be very hard without the tank (it's hard even when taking it slowly).

Helicopter to the end - https://www.youtube.com/watch?v=YWbME65q8XU
There are several self-exploding guys near the middle of the first water section, so the route shown here is both the safest and the fastest (at least currently). The fuel drop is inconsistent, but seems to be ~50%. It's not known (has not been researched) if this can somehow be manipulated.
After collecting the extra fuel, it's possible to take a more direct route than what's shown here, but not by much. 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 it seems to be in one of six locations (this is not of great importance, but hasn't been properly verified). The best you can do is to throw two grenades from two different places as shown in this video. With better luck, you will reveal the exit after the first throw and be able to finish the level earlier.

Level 4

Foot1 to tank - https://www.youtube.com/watch?v=5-mHQfMMjVM
The area before arriving at the pools is consistent. 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 in the pool area.

Tank to foot2 - https://www.youtube.com/watch?v=DYI-ShDF8dk
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.
This section would be extremely hard to do on foot.c

Foot2 to helicopter - https://www.youtube.com/watch?v=oqtI-QI1LE0
Random enemies can appear on the left side of the water section, but can quite easily be dealt with when it's the case. The rest is not random quite easy to execute. The route through the barrel area can be done faster and the big loop back before the helicopter obviously consumes a lot of time. However, from testing, this seems to give quite good chances for a fuel can drop near the helicopter. This has purely been tested by experimenting with various routes from various save states, but there is no hard proof that this optimizes the chances for the right drop. The drops contained inside the walls are determined a little before they appear on screen. By turning around and walking backwards, it's quite evident that the memory gets more and more corrupted. That's where the idea of the loop back comes from.

Helicopter to the end - https://www.youtube.com/watch?v=hCg_4BE0B0E
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 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), but it's still not 100% safe.
The last boss normally takes 10 hits. Once it starts to explode, you can start walking towards the golden heart. Occasionally, the boss takes 17 hits, which is quite the time loss. The reason for this is unknown.