Lead Impact on Wild Methods in Emerald

Gist: Understanding why the lead impacts which Wild method is triggered.

Prerequisite

Having read Methods 1-4 and VBlanks

Pokémon Wild Encounter (Simplified version)

Here's a simplified example of the code executed on a wild encounter:

Step	Cycles	Total Cycles
1- Update audio & visual	+ 50K	50K
2- Miscellaneous updates	+ 5K	55K
3- Prepare wild encounter	+ 15K-115K	70K-170K
4- Generate valid PID	+ 10K	80K-180K
5- Create Pokémon without IVs	+ 115K	195K-295K
6- Generate Def, Atk, HP IVs	+ 1K	196K-296K
7- Assign Def, Atk, HP IVs	+ 39K	235K-335K
8- Generate SpD, SpA, Spe IVs	+ 1K	236K-336K
9- Assign SpD, SpA, Spe IVs	+ 39K	275K-375K

Reminder: When the cycle count reaches 280K, a VBlank occurs. VBlank occurring during step "5- Create Pokémon without IVs" will cause Wild-2 method. VBlank at step "7- Assign Def, Atk, HP IVs" causes Wild-4 method. VBlank occurring afterwards or no VBlank will cause Wild-1. During the step "3- Prepare wild encounter", the code fetches the ability of the lead Pokémon multiple times. This takes a variable number of cycles depending on the lead. By using a carefully selected lead, we can control which wild method will be triggered.

Step	Fastest Lead Wild-1	Fast Lead Wild-4	Slow Lead Wild-2
1- Update audio & visual	50K	50K	50K
2- Miscellaneous updates	55K	55K	100K
3- Prepare wild encounter	70K (fastest)	120K (fast)	170K (slow)
4- Generate valid PID	80K	130K	180K
5- Create Pokémon without IVs	195K	245K	295K (VBlank)
6- Generate Def, Atk, HP IVs	196K	246K	...
7- Assign Def, Atk, HP IVs	235K	285K (VBlank)	...
8- Generate SpD, SpA, Spe IVs	236K ...	...	...

Determining if a lead is slow or fast

There are 2 factors that determine if a lead is slow or fast: If the lead is an egg, a lot of the Pokémon generation logic is skipped, which saves a lot of cycles. The PID of the egg has no impact. If the lead is not an egg, the code performs a modulo operation on its PID to obtain its ability. The number of cycles taken by this modulo operation depends on the PID value. A typical wild encounter triggers the modulo operation 80 times. This big cycle difference is why we can use a lead to control which wild method is triggered.

Pokémon Wild Encounter (Complete version)

In reality, the wild encounter logic is more complex than the simplified version above, because most steps take a variable number of cycles. Fortunately, in most cases, the number of cycles taken by each step can be precalculated.

Step	Cycles	Type	Depends on
1- Update audio & visual	45K-65K	Unpredictable	Audio frame
2- Miscellaneous updates	5K	Precalculable	-
3- Prepare wild encounter	15K-115K	Controllable	Lead
4- Generate valid PID	1K-1000K	Precalculable	RNG state (# PID rerolls)
5- Create Pokémon without IVs	36K-125K	Precalculable	Generated Pokémon PID
6- Generate Def, Atk, HP IVs	1K	Precalculable	-
7- Assign Def, Atk, HP IVs	11K-43K	Precalculable	Generated Pokémon PID
8- Generate SpD, SpA, Spe IVs	1K	Precalculable	-
9- Assign SpD, SpA, Spe IVs	Doesn't matter

The step with the most variability is "4- Generate valid PID". In that step, the game generates a random nature, and then a PID is generated until it matches the wanted nature. In some cases, this can take a lot of retries. If the lead has the Cute Charm ability, then the generated PID must also match the wanted gender, resulting in even more retries. If that step takes too many cycles (ex: 150K cycles), triggering Wild-1 might not be possible, even with the fastest possible lead. Using a fast lead only increases the likelihood of Wild-1. Similarily, if that step is too fast (ex: 1K cycles), triggering Wild-2 might not be possible, even with the slowest lead. The cycles of the step "1- Update audio & visual" depends on the audio frame, which depends on the frame the savefile is loaded and other factors. It is impossible to predict on retail and will vary between each RNG manipulation attempt.

VBlank when generating a valid PID

A VBlank occurring during the step "4- Generate valid PID" would result in either Wild-3 or Wild-5. Those methods will be covered in the next article.

Credits