According to Volo in Pokémon Legends: Arceus, there are two legends as to Lake Valor's origins. The first says it was formed from a volcano crater, as Lake Verity was, while the second says it was carved out in an ancient Pokémon battle.
In Pokémon: Legends: Arceus, the player travels to Lake Valor for Mission 15: "The Trial of Lake Valor". In it, the players fights an Alpha Overqwil and catches or defeats it. Azelf appears after and tests the player's will by having them throw balms at Azelf as it dodges every attempt. After showing their will to keep going, Azelf gives the player Azelf's Fang, one of the materials required to craft the Red Chain.
As part of Request 89: "The Diamond Clan's Treasure", the player battles Adaman of the Diamond Clan at Lake Valor, earning the Adamant Crystal from him after winning.
During the events of Pokémon Diamond, Pearl, and Platinum and Pokémon Brilliant Diamond and Shining Pearl, Team Galactic uses a Galactic Bomb to dry up the lake. The resulting earthquake is felt in Canalave City, located at the opposite side of Sinnoh. While dried-up, what appears to be the remains of a river that flows into the lake is located to the northwest of the lake. When the lake is restored, the remnants of the river disappear and are replaced by trees. While the lake is dried up, the cavern entrance is at the level of the lakebed, but while it is filled, the entrance is at the water level.
After DialgaDBD/PalkiaPSP/GiratinaPt has been dealt with at Spear PillarDPBDSP/the Distortion WorldPt, the lake will have been rejuvenated and can be Surfed on.
Items
Item
Location
Games
HP Up
In the northwest while the lake is dry, next to the pile of Magikarp (hidden) (missable)
D P Pt BD SP
TM25 (Thunder)
At the right edge of tall grass in the southeast part of the lake (requires Surf)
D P Pt BD SP
Marsh Balm
Given by Azelf prior to its trial during Mission 15: "The Trial of Lake Valor"
LA
Azelf's Fang
Given by Azelf after clearing its trial during Mission 15: "The Trial of Lake Valor"
LA
Draco Plate
Reward for catching Azelf during Mission 21: "The Plate of the Lakes" (only if Uxie and Mesprit were caught first)
LA
Adamant Crystal
Given by Adaman after defeating him during Request 89: "The Diamond Clan's Treasure"
LA
Comet Shard ×3
Reward for completing Request 89: "The Diamond Clan's Treasure"
LA
Pokémon
Generation IV
Pokémon
Games
Location
Levels
Rate
Psyduck
D
P
Pt
Grass
35-36
20%
Psyduck
D
P
Pt
Grass
38-39
15%
Golduck
D
P
Pt
Grass
40-41
15%
Noctowl
D
P
Pt
Grass
34, 36
0%
0%
20%
Staravia
D
P
Pt
Grass
34-36
25%
25%
0%
Staravia
D
P
Pt
Grass
35
0%
0%
5%
Staravia
D
P
Pt
Grass
38, 40
35%
Bibarel
D
P
Pt
Grass
34-36
45%
Bibarel
D
P
Pt
Grass
39, 41
35%
Chingling
D
P
Pt
Grass
35-36
10%
Surfing
Psyduck
D
P
Pt
Surfing
20-40
90%
Psyduck
D
P
Pt
Surfing
20-30
90%
Golduck
D
P
Pt
Surfing
20-40
10%
Fishing
Magikarp
D
P
Pt
FishingOld Rod
3-10
100%
Magikarp
D
P
Pt
FishingOld Rod
3-15
100%
Goldeen
D
P
Pt
FishingGood Rod
10-25
45%
Goldeen
D
P
Pt
FishingGood Rod
15-20
40%
Seaking
D
P
Pt
FishingGood Rod
25-35
5%
Magikarp
D
P
Pt
FishingGood Rod
10-25
55%
Seaking
D
P
Pt
FishingSuper Rod
20-50
45%
Seaking
D
P
Pt
FishingSuper Rod
30-55
45%
Gyarados
D
P
Pt
FishingSuper Rod
30-55
55%
Swarm
Lickitung
D
P
Pt
Swarm
34, 36
40%
Special Pokémon
Wobbuffet
D
P
Pt
Poké Radar
35, 36
22%
Wobbuffet
D
P
Pt
Poké Radar
38, 40-41
22%
Lunatone
D
P
Pt
Dual-slotSapphire
35
8%
Lunatone
D
P
Pt
Dual-slotSapphire
40-41
8%
Solrock
D
P
Pt
Dual-slotRuby
35
8%
Solrock
D
P
Pt
Dual-slotRuby
40-41
8%
A colored background means that the Pokémon can be found in this location in the specified game. A white background with a colored letter means that the Pokémon cannot be found here.
Generation VIII
Brilliant Diamond and Shining Pearl
Pokémon
Games
Location
Levels
Rate
Psyduck
BD
SP
Grass
35-36
20%
Noctowl
BD
SP
Grass
34, 36
0%
0%
20%
Staravia
BD
SP
Grass
34, 36
20%
20%
0%
Staravia
BD
SP
Grass
35
5%
Bibarel
BD
SP
Grass
34-36
45%
Chingling
BD
SP
Grass
35-36
10%
Surfing
Psyduck
BD
SP
Surfing
20-40
90%
Golduck
BD
SP
Surfing
20-40
10%
Fishing
Magikarp
BD
SP
FishingOld Rod
3-10
100%
Goldeen
BD
SP
FishingGood Rod
10-25
45%
Magikarp
BD
SP
FishingGood Rod
10-25
55%
Seaking
BD
SP
FishingSuper Rod
20-50
45%
Gyarados
BD
SP
FishingSuper Rod
30-55
55%
Swarm
Lickitung
BD
SP
Swarm
34, 36
40%
Special Pokémon
Wobbuffet
BD
SP
Poké Radar
35-36
22%
A colored background means that the Pokémon can be found in this location in the specified game. A white background with a colored letter means that the Pokémon cannot be found here.
Legends: Arceus
Location of Lake Valor in Hisui
Pokémon
Levels
AlphaLevels
Time of day
Weather
Golbat‡
25-28
40-43
✔
✔
Graveler‡
25-28
40-43
✔
✔
Gastly‡
17-24
32-39
✔
✔
Haunter‡
33-36
48-51
✔
✔
Onix‡
25-28
40-43
✔
✔
Combee‡
17-20
32-25
✔
✔
Vespiquen‡
33-36
48-51
✔
✔
Fixed Alpha
Whiscash
64
✔
✔
In the air
Carnivine‡
25-28
40-43
✔
✔
Shaking trees
Burmy‡ Sandy Cloak
16-19
31-34
✔
✔
Shaking ore deposits
Graveler
25-28
40-43
✔
✔
Water
Barboach
26-29
41-44
✔
✔
Whiscash
53-56
68-71
✔
✔
Non-fixed alpha Pokémon do not spawn until the player quelled the frenzy of the subregion's noble.Some of the Pokémon marked with (‡) may only spawn near the area's borders.
Special encounters
Pokémon Diamond and Pearl
Azelf in Valor Cavern
An Azelf appears in Valor Cavern after dealing with DialgaD/PalkiaP. If run from, it respawns upon leaving the area.
An Alpha Overqwil can be caught during Mission 15: "The Trial of Lake Valor", which becomes available after completion of Mission 13: "Disaster Looming". Once defeated, Overqwil does not respawn. It is coded to never be Shiny.
Azelf can be caught during Mission 21: "The Plate of the Lakes", which becomes available after completion of Mission 20: "The Researcher of Myths". If fled from or knocked out, it respawns immediately without leaving the area. It is coded to never be Shiny.