In the AI code there is a function known as "WarnHideLvl" that gives the AI a value which is what they assume your facedown cards are. This value is mainly defined by what their current life points are, but also the amount of monsters they have on the field effects this. Because of the nature of speedrunning, the most important value is what they assume your facedowns are when they have 4000 LP and they do NOT have a 'high' amount of monsters. This guide will provide a quick and handy list and then go into more detail about why this matters. If the opponent has a monster on the field, and it does not attack your facedown, that means that their monster has a lower attack than what their WarnHideValue is. You can use this to help determine what an opponents facedown monster is (if you are certain it is a monster). For example, Mai's default WarnHideLvl is 1500. Because the only monster she can play on Mountain that is weaker than 1500 is an unequipped Kanan the Swordmistress, if she opens with a card on her right and then moves it forward, but then DEFENDS with it if you have a facedown cards within 2 spaces of it, you can conclude that this card she opened with is a Kanan the Swordmistress without even needing to flip that card face up. Other uses include playing a high atk/def monsters two spaces away from an enemy facedown monster on duels with a 0 WarnHideLvl (Weevil in particular) as they can flip a super weak monster up and attack into your monster and you can possibly deal a very significant amount of LP damage in a situation you might not be able to otherwise. Another property of opponents with a WarnHideLvl of zero is that by seeing your facedowns as 0, they do not feel threatened by it and do not move away from facedowns. There are multiple applications of this also shown below in text.

Please note that enemy AI deck leaders themselves do not use WarnHideLvl to determine if your face down card is a threat or not - enemy deck leaders will not react to a face down card unless it is a monster with an atk/def value of over 0 (atk/def seems to correspond to if the monster itself is actually in atk or def position). However, WarnHideLvl is still useful for all other applications, and still determines if your opponent attacks or doesn't attack into your facedown regardless of if the enemy reacts to your facedown card by moving or NOT moving their deck leader.

Here is a basic list of values that your opponent's AI will assume your face down cards are:

Weevil : 0

Rex : 0

Richard : 0

Tea : 0

Tristan : 0

Joey : 1000

Yugi : 1000

Keith : 1000

Isthar : 1000

Seto : 1500

Panik : 1500

Labruler: 1500

Mai : 1500

Bakura : 1500

Mako : 1500

Grandpa : 1500

Necro : 2000

Shadi : 2000

Pegasus : Knows the atk/def of your facedowns

MFL C : Knows the atk/def of your facedowns

MFL SK : Knows the atk/def of your facedowns

So explaining how this effects a speedrun is more important than why AI are programmed like this, so I will do that first. The most important example is Seto Kaiba. If you run this game and understand the Seto strategy of putting a card in the middle of the field, you can manipulate Seto Kaiba to play a monster to his right and move two spaces forward. This occurs because Seto Kaiba had a monster in his opening hand that he wanted to play infront of him, but then he decides to play the monster on his next available tile (to his right) to avoid it being placed in a dangerous position - a tile within 2 spaces of your monster in the middle. If you have a monster of 2200 attack such as a face up Great Mammoth, if he wants to play anything weaker than this value, he will play it to the right, move forward, then you attack him on turn 2 and the manip is successful.

But if you do not have a significant amount of damage, he is unlikely to move forward. If you consider having a hand full of monsters weaker than 1500 attack, you can leave the card face down in the middle and Seto Kaiba's AI will assume your face down card in the middle is 1500 attack. So, if he wants to play a monster such as Mystic Horseman, he believes it is a bad idea to play it near a card he assumes to be 1500 attack, so he will play it to the right and move forward and you can successfully manipulate him to move to the middle tile even if you don't even have a monster with an attack value of any kind in the middle of the field.

The thing about enemies who have a value of 0 is that they will just always attack your facedowns if you have a monster available to attack. Because some of these duelists such as Tea and Weevil have weak cards, they can attack into your monsters and be destroyed, allowing you to deal a lot of lifepoint damage. Tea's basic strategy is quite simple - it is enabled by the fact she will always attack your facedowns (unless her monster is reduced to 0 atk if you put Yami terrain on the field). Another application is against Weevil, you can defend with a high ATK/DEF monster 2 spaces away from one of his facedown cards you believe to be a monster. If this happens to be something weak such as Petit Moth (800 atk/700 def on Forest) and you defend with a Great Mammoth (2200/1800), he will attack into your Great Mammoth and you will deal 1000 damage when it attacks you, then the next turn you will deal 1400 LP when you successfully attack it.

Another instance of why this matters are crush tiles, in particular on the Bakura and Shadi maps. Because Bakura's WarnHideLvl is 1500 and Shadi's is 2000, they will literally never attack your facedown cards on Crush, because they will not move any monster of theirs that has attack higher than 1500/2000 onto Crush tiles because they believe it will die on that tile. The exception to this is Bakura may attack your card to take control of it with Laughing Flower.

On a duelist such as Mai, if she plays a monster to her left on the opening turn with no Equips, it is possible for it to be a base attack Kanan the Swordmistress (1400 on Mountain). Because this is the only monster she has that is not 1500 or higher ATK on mountain, if she plays a monster to her right on the first turn, then eventually decides to defend with it when it is within 2 spaces of a facedown, you can assure yourself that is is a Kanan the Swordmistress and identify it as an Earth Warrior with 1400 atk/def (as long as you are 100% sure that is a monster by virtue of her having played it to her right and moved it forward one tile initially).

Tristan will move away from a monster you attack it with. If you place a monster facedown to the right of a monster you attacked him directly with it, you may assume he would move in the opposite direction because he wouldn't want to move in the direction of where your facedown monster could hit it, but, because he reads the face down cards attack as zero, he ignores it as a 'threat' (like a face up monster would normally force him to move in the opposite direction) and so in Tristan if you are not able to kill him in two hits with the first monster you attack him with, you can potentially play a facedown to the right tile of that first monster you attacked him with, and he will move left (as he normally does move away from one face up monster infront of him) into it, rather than away from it.

You can also for example place a facedown monster infront of Richard, and he will not move away from it (even if he isn't protected by an Acid Trap Hole) because he does not see it as a threat. In a situation where you need at least one more turn to kill him, you can use this to keep him on the same spot, so that the next turn you can attack him directly and then play another monster on top of that monster and attack him again as he hasn't moved away and played/moved other monsters in the way. Plays like this also allow you to fuse a monster on the same tile after attacking, for example if you have a face down Pumpking infront of him, you can attack him for 1800, then fuse a Mammoth Graveyard over it to create 2200 and kill him in one turn. This would still mean you need 2 turns to kill him as you pass the first of two turns without attacking him, but having a monster face down and then following by OTKing him removes him being able to react in a meaningful way and helps secure the win easier.

Another example of where this is useful is that AI generally will double tap their monsters next to yours if the attack value is the same as your monsters, rather than defending with them OR attacking them (duelists generally dont move a monster away if it will still be within attacking range if your monster has bonus movement). However, AI can double tap this even if they don't know your monsters atk/def, if they assume it has the same value. If you are playing Labruler and he leaves a monster infront of your facedown and double taps it in attack mode, it is because he assumes your facedown is 1500 and his monster is 1500 attack exactly. If it was weaker than 1500, it would defend, and if it was over 1500, he would attack your facedown with it. So, if you ever see this occur on Labruler when you springboard towards him, and he doesnt defend your attack you but leaves his monster in attack mode facedown on the next tile to your face down, it is because it is specifically Kojicocy, as that is the only monster he has with exactly 1500 attack and so now you know exactly what that card is. If he defends, it is below 1500 which means it could be any of his cards weaker than 1500, including something potentially really devastating such as Dream Clown - but it is more likely to be something rather innocuous such as Cockroach Knight or some other weak insect card.

There are lots of points where this value is really important, so try to remember the value that your opponent's AI predicts your facedowns to be, and treat your own facedowns as if they have that exact ATK/DEF to help yourself determine what monsters your opponent has on the field. If the opponent has a monster on the field, and it does not attack your facedown, that means that their monster has a lower attack than what their WarnHideValue is.

What is less important but may clear things up is that, this is what determines how 'aggressive' the AI is. Early duelists (Weevil, Rex, Tea, Tristan) and Heishin who claims to be a beginner/inexperienced have values of zero because they are not as 'smart'. On the contrary you have a duelist such as Shadi who assumes your facedowns are 2000 as a means to only ever attack your facedowns with a monster that is rather powerful (above 2000 attack). The value for most AI is 1500, but remembering this value can really make a difference. If you have a facedown dragon on Mountain, Yugi can flip up a Feral Imp from the Yami tile two spaces infront of his deck leader, and attack it, because he assumes your Dragon is 1000 attack and that he can beat it with 1300 attack. If he plays something such as a Kuriboh which has an attack lower than 1000, he will choose to defend with it instead of putting it next to a a card you own that he believes is 1000 attack. With non-Yami monsters he will move it one space towards your monster because he thinks he can take it on. This also avoids something such as the opponent attacking you with a 500 attack card when they have 100 LP because attacking even into a defense mode Komouri Dragon would kill them.

The complete list of WarnHideLvls is below. Remember that generally in speedrunning the enemy rarely has this value affected by having 'lots of monsters' out because you generally kill the opponent before they reach that amount of monsters on the field. However, it is important to know the high number as an opponent such as Seto/Yugi will not attack into your facedowns unless they play a very strong monster. A realistic situation is Seto or Yugi being in LP range to trigger destiny draw, they will not attack you with anything but their highest attack monsters on this turn.

N/A: Pegasus, Skull Knight, Chakra

Weevil, Rex, Richard, Tea, Tristan read your facedowns as 0 at all times.

For everyone else, there are 3 values in the form of:

High (the highest number) - What your opponents think your facedowns are when they have "Low LP" (Low LP is listed corresponding to the duelist in the below list)

Mid (the middle number - this is the default in the basic form list

Low (the lowest number) - this is when the AI has more than their low LP and has 'lots of monsters' (this value depends on the AI too and is in the below list) - they will assume your cards are all really weak and play aggressively by attacking you with even some of their weaker-midrange cards. This is the least important value as in a speedrun your opponent isn't likely to have more than 3 monsters on the field, but the value is there anyways.

So for example if seto has 1200 LP or less, he will think all of your facedown cards have 2500 attack, therefore he will not attack your facedown cards with a monster weaker than this value. (Basically if someone has about 1200 or lower attack, they think your facedown cards have a higher attack, so they wont attack into your facedown cards unless they have a really high attack card that theyre more confident will beat your card)

If he has above 1200 LP, he will assume your facedown card has 1500 attack.

If he has above 1200 LP and at least 4 monsters on the field, he will assume your facedowns have 750 attack, meaning attack monsters with any card he has above 750.

Seto: low LP means 1200 or lower, lots of monsters means at least 4, values are 2500/1500/750

Darkness-ruler: low LP means 2000 or lower, lots of monsters means at least 4, values are 2400/1500/750

Lab-ruler: low LP means 1000 or lower, lots of monsters means at least 4, values are 1700/1500/750

Mai: low LP means 1500 or lower, lots of monsters means at least 4, values are 2000/1500/750

Joey: low LP means 1200 or lower, lots of monsters means at least 4, values are 1500/1000/500

Bakura: low LP means 1200 or lower, lots of monsters means at least 5, values are 2000/1500/750

Yugi: low LP means 1200 or lower, lots of monsters means at least 4, values are 2000/1000/500

Necromancer, Shadi, DMK: low LP means1200 or lower, lots of monsters means at least 4, values are 2400/2000/1000

Mako, Jasper: low LP means 1200 or lower, lots of monsters means at least 5, values are 2400/1500/750

Keith, Ishtar: low LP means 1000 or lower, lots of monsters means at least 3, values are 2000/1000/500