Wild Pokémon Mechanics

Pokémon Let's Go Pikachu and Let's Go Eevee feature a change to the Pokémon wild encounters. Wild encounters have changed considerably from past games. First, the Pokémon appear on the overworld and encounters start when you walk into it. Each Pokémon may sometimes have an aura. If it's a red aura, the Pokémon will be larger than normal. If it's a blue aura, it'll be smaller than normal. If it has stars above its head and the Shiny Colours, it will be Shiny.

Each area has got a specific limit to the amount of spawns that can be available at any one time, and areas with large spawn areas such as caves and water routes can spawn Pokémon off-screen, otherwise they spawn around the patches of grass. Each area also has a maximum spawn duration which is typically around 150 seconds. However, Pokémon can despawn ahead of that if the spawning of another Pokémon is calculated to happen. Below is a chart showing all the maximum spawns in each area.

AreaMaximum Spawns
GrassWaterSky
Route 1 10   3
Route 2 - South 4   3
Route 2 - North 4   3
Route 3 6   3
Route 4 - West     3
Route 4 - East 4 3 3
Route 5 6   3
Route 6 6 3 3
Route 7 4   3
Route 8 4   3
Route 9 6   3
Route 10 4 5 3
Route 11 8 3 3
Route 12 4 5 3
Route 13 4 5 3
Route 14 4   3
Route 15 6   3
Route 16 4   3
Route 17 8   3
Route 18 4 3 3
Route 19   7 3
Route 20 - East   9 3
Route 20 - West   9 3
Route 21 4 7 3
Route 22 6 3 3
Route 23 8 3 3
Route 24 4 3 3
Route 25 4 3 3
Viridian Forest 20    
Diglett's Cave 8    
Mt. Moon - 1F 10    
Mt. Moon - B1F 5    
Mt. Moon - B2F 10    
Cerulean Cave - 1F 10 3  
Cerulean Cave - 2F 10    
Cerulean Cave - B1F 10 3  
Rock Tunnel - 1F 10    
Rock Tunnel - B1F 10    
Pokemon Tower - 3F 2    
Pokemon Tower - 4F 2    
Pokemon Tower - 5F 4    
Pokemon Tower - 6F 6    
Power Plant 10    
Seafoam Islands - 1F 5    
Seafoam Islands - B1F 5    
Seafoam Islands - B2F 5    
Seafoam Islands - B3F 5 5  
Seafoam Islands - B4F 5 5  
Pokemon Mansion - 1F 8    
Pokemon Mansion - 2F 8    
Pokemon Mansion - 3F 8    
Pokemon Mansion - B1F 8    
Victory Road - 1F 10    
Victory Road - 2F 10    
Victory Road - 3F 10    

However, when you do interact with Wild Pokémon, you no longer battle to weaken them. Instead, you go to a capture screen.

Catch Calculation

This screen is like the capture in Pokémon GO where you have the Pokémon and just throw the ball at it. This is done with the Joy-Cons motion detection in Docked Mode or using motion or the control stick in Handheld mode. The better the throw into the circle around the Pokémon, the better the chance of capture

Catch rate is a completely different situation to the previous and subsequent Pokémon games with the Pokémon's Catch Rate being modified through a variety of means.

ShakeChance

65535 / (255/ModifiedCatchRate)1/5.33

A number generator is then decided between 0 and 65535. If the number is less, then it's success. 4 shakes mean the capture is successful.

Modified Catch Rate

1.85√(SpeciesCatchRate * (Players x Berry) * 1.25)

There's another method that helps the catch rate. As you increase your catches of the same species of Pokémon, the capture rate will increase. This does not have to be within a combo.

Catch Progress

4√(10000/((1000-TotalCaught)/100)*CP+1)

The final Spceies Catch Rate shown is showcased by the Ring

Ring Catch Rate
Red0-32
Orange32-64
Yellow64-128
Green128-255

In addition to that, if you're playing in local co-op play and both players throw the ball and it hits at the same time, you'll get a boost due to the Synchronized capture.

Players

NumberOfPlayers * (CatchProgress*(#8730;((Player1Ball + Player2Ball)/NumberofPlayers)*NewbieModifier)3)

Newbie Modifier is 1 as standard but 1.5 if you haven't reached Viridian Forest

Finally, there are three different berries that improve the rate of capture. Each Berry has a higher boost making capture a lot easier than standard. The technique also factors in, where if you hit the Poké Ball inside the circle as it goes down, you'll get a special bonus with an increase

Berry #8730;(Technique * Berry)
Picture Name Effect
Razz Berry *1.5
Silver Razz Berry *2.25
Golden Razz Berry *4
Technique Effect
None*1
Nice*1.5
Great*2
Excellent*2.5

Experience

Experience gained works the same as before, using the wild Pokémon's level and base experience in order to determine how many experience you gain, scaled depending on your Pokémon's level. However, there are ways to get even more experience. When you cach a Pokémon, you now get various experience bonuses based upon how well your capture went. Each bonus is then multiplied in from the standard 100% (and rounded down to 1 Decimal Place) in order to get bonuses even as high as *80

Picture Name
Combo Throw *1.1 (Combo 2-10)
*1.5 (Combo 11-20)
*2 (Combo 21-30)
*2.5 (Combo 31-40)
*3 (Combo 41+)
Excellent Throw *2.5
First Throw *1.5
Great Throw *2
Nice Throw *1.5
Size Bonus (L or S) *1.5
Size Bonus (XL or XS) *4
Synchro Bonus (Co-Op Only) *2
Technique Bonus *1.1