Sorry if this post is really long.
http://www.serebii.net/pokearth/kanto/route3.shtml#4th
In the HeartGold encounters by walking section, the Night slot for Jigglypuff is listed under the Day section.
http://www.serebii.net/pokearth/kanto/route4.shtml#4th
In the HeartGold encounters by walking section, the Night slot for Jigglypuff is listed under the Day section.
http://www.serebii.net/pokearth/kanto/route6.shtml#4th
The HeartGold encounters by walking section matches the encounters of Route 5, not Route 6.
In the SoulSilver encounters by walking section, the Morning slot for Abra is listed under the Day section.
http://www.serebii.net/pokearth/kanto/route9.shtml#4th
In the SoulSilver encounters by walking section, the sum of the encounter rates for both the Morning and Day sections add up to 110%, not 100%.
http://www.serebii.net/pokearth/kanto/route19.shtml#4th
Not really a mistake, but in the Old Rod section, there are separate sections for Morning, Day, and Night, even though Old Rod encounters don't change depending on time of day.
Not really a mistake, but in the Good Rod and Super Rod sections, the primary divisions are based on time of day instead of version. Aren't primary divisions usually based on version?
http://www.serebii.net/pokearth/kanto/ceruleancave.shtml#1st
In the first generation, Cerulean Cave was called Unknown Dungeon.
http://www.serebii.net/pokearth/kanto/ceruleancave.shtml#hgss-1f
Not really a mistake, but in the encounters by walking at night section, Machoke is listed after Electrode and Wobbuffet in both the HeartGold and SoulSilver sections, even though its encounter rate is higher.
http://www.serebii.net/pokearth/kanto/diglett'scave.shtml#frlg-b1f
Not really a mistake, but in the encounters section for FireRed, Diglett is listed after Dugtrio, even though its encounter rate is higher.
http://www.serebii.net/pokearth/kanto/victoryroad.shtml#hgss-1f
In the encounters by walking section, the sum of the encounter rates for both the HeartGold and SoulSilver sections add up to 90%, not 100%.
http://www.serebii.net/pokearth/johto/route30.shtml#c
In the encounters by walking during the day section, there is a slot for Marill. That slot should contain Hoppip, not Marill.
http://www.serebii.net/pokearth/johto/route34.shtml#4th
Not really a mistake, but in the Old Rod section, there are separate sections for Morning, Day, and Night, even though Old Rod encounters don't change depending on time of day.
Not really a mistake, but in the Good Rod and Super Rod sections, the primary divisions are based on time of day instead of version. Aren't primary divisions usually based on version?
http://www.serebii.net/pokearth/johto/route35.shtml#4th
In the Surfing section, the sum of the encounter rates for both the HeartGold and SoulSilver sections add up to 91%, not 100%.
http://www.serebii.net/pokearth/johto/route37.shtml#4th
In the SoulSilver encounters by walking section, the Day section contains a slot for Ekans. That slot should contain Stantler, not Ekans.
http://www.serebii.net/pokearth/johto/route39.shtml#4th
The SoulSilver encounters by walking section matches the encounters of Route 38, not Route 39.
http://www.serebii.net/pokearth/johto/route40.shtml#4th
Not really a mistake, but in the Old Rod section, there are separate sections for Morning, Day, and Night, even though Old Rod encounters don't change depending on time of day.
Not really a mistake, but in the Good Rod and Super Rod sections, the primary divisions are based on time of day instead of version. Aren't primary divisions usually based on version?
http://www.serebii.net/pokearth/johto/route42.shtml#4th
In the HeartGold encounters by walking section, the Night section contains a slot for Spearow. That slot should contain Zubat, not Spearow.
http://www.serebii.net/pokearth/johto/route45.shtml#gs
The Good Rod and Super Rod sections for both Gold and Silver list Pokemon as being at Level 20 with the Good Rod and at Level 40 with the Super Rod. In Route 45 in Gold and Silver, all Pokemon found by fishing with any rod are at Level 10.
http://www.serebii.net/pokearth/johto/route45.shtml#c
The Good Rod and Super Rod sections list Pokemon as being at Level 20 with the Good Rod and at Level 40 with the Super Rod. In Route 45 in Crystal, all Pokemon found by fishing with any rod are at Level 10.
http://www.serebii.net/pokearth/johto/belltower.shtml#hgss-2f
In the HeartGold encounters by walking section, the Day slot for Rattata is listed under the Morning section.
http://www.serebii.net/pokearth/johto/cherrygrovecity.shtml#4th
Not really a mistake, but in the Old Rod section, there are separate sections for Morning, Day, and Night, even though Old Rod encounters don't change depending on time of day.
Not really a mistake, but in the Good Rod and Super Rod sections, the primary divisions are based on time of day instead of version. Aren't primary divisions usually based on version?
http://www.serebii.net/pokearth/johto/cianwoodcity.shtml#c
Eusine's title is listed as Mystical Man, but it's actually supposed to be Mysticman.
http://www.serebii.net/pokearth/johto/cianwoodcity.shtml#4th
Not really a mistake, but in the Old Rod section, there are separate sections for Morning, Day, and Night, even though Old Rod encounters don't change depending on time of day.
Not really a mistake, but in the Good Rod and Super Rod sections, the primary divisions are based on time of day instead of version. Aren't primary divisions usually based on version?
http://www.serebii.net/pokearth/johto/olivinecity.shtml#4th
Not really a mistake, but in the Old Rod section, there are separate sections for Morning, Day, and Night, even though Old Rod encounters don't change depending on time of day.
Not really a mistake, but in the Good Rod and Super Rod sections, the primary divisions are based on time of day instead of version. Aren't primary divisions usually based on version?
http://www.serebii.net/pokearth/johto/unioncave.shtml#gs-1f
Sandshrew can't be found in Union Cave in Silver.
http://www.serebii.net/pokearth/johto/unioncave.shtml#gs-b1f
Sandshrew can't be found in Union Cave in Silver.
http://www.serebii.net/pokearth/johto/unioncave.shtml#hgss-1f
Not really a mistake, but in the encounters by walking section for SoulSilver, Rattata is listed after Geodude, even though its encounter rate is higher.
http://www.serebii.net/pokearth/johto/unioncave.shtml#hgss-b1f
Not really a mistake, but in the encounters by walking section for SoulSilver, Rattata is listed after Geodude, even though its encounter rate is higher.
http://www.serebii.net/pokearth/johto/unioncave.shtml#hgss-b2f
Not really a mistake, but in the encounters by walking section for both HeartGold and SoulSilver, Raticate is listed after Zubat, even though their encounter rates are the same and Raticate's National Dex number is lower.
Not really a mistake, but in the Old Rod section, there are separate sections for Morning, Day, and Night, even though Old Rod encounters don't change depending on time of day.
Not really a mistake, but in the Good Rod and Super Rod sections, the primary divisions are based on time of day instead of version. Aren't primary divisions usually based on version?
http://www.serebii.net/heartgoldsoulsilver/movetutors.shtml
The Draco Meteor tutor isn't mentioned on this page.
http://www.serebii.net/heartgoldsoulsilver/headbutt.shtml
Natu isn't mentioned in the list of Pokemon that can be found with Headbutt.