Underleveled Pokémon

In the games, underleveled Pokémon are evolved forms at a level less than the required level to evolve. This is often a result of game balancing in the early areas of the games, in-game trades, and special distribution Event Pokémon. Occasionally NPCs will also battle with underleveled Pokémon.

Obtainable Underleveled Pokémon
The following tables are for Pokémon obtainable through normal gameplay, divided by generation. Listed are the name and National Dex number of the Pokémon, the level they normally evolve at, the lowest obtainable level (although some can be found at a level higher than this but still be underleveled), the game title found in, and the location in-game. Pokémon with significant differences in details can be listed more than once, and Pokémon without differences but found in more than one place have a "multiplication" in their location, for simplicity and sorting.

Pokémon obtained through in-game trades before Generation V were the same level as the Pokémon offered by the player. This makes some underleveled Pokémon possible, especially when obtaining the offered Pokémon from another generation or title (such as by breeding in Generation II then trading back to Generation I). These Pokémon have a "T" in their obtainable level column instead of a number.

Pokémon obtainable outside of normal gameplay a listed below the main table for that generation.

Generation III
Some special distribution Event Pokémon are underleveled. These are now unavailable through legitimate methods.
 * Gotta Catch 'Em All Event Magmar (2006 Japan)
 * Gotta Catch 'Em All Event Electabuzz (2006 Japan)
 * Toys 'R' Us Trade and Battle Day Haunter (2004 USA)

Diamond, Pearl, and Platinum
Some special distribution Event Pokémon are underleveled. These are now unavailable through legitimate methods.
 * Toys 'R' Us Dragonite (2008 USA)
 * Strongest Pokémon Distribution Dragonite (2008 Japan)

Generation V
Underleveled Pokémon can be found in Hidden Grottos in Pokémon Black and White Version 2. These Pokémon drop with very low chance into an empty Grotto, meaning there is a possiblity that they will never be seen by a player.
 * Herdier - Floccesy Ranch at level 10-15
 * Amoonguss - Abundant Shrine at level Lv 35-40
 * Leavanny - Lostlorn Forest at level 20-25
 * Muk - Unova Route 9 at level 35-40
 * Garbodor - Unova Route 9 at level 35-40

Some special distribution Event Pokémon are underleveled. These are now unavailable through legitimate methods.
 * Pokémon Game Show - Lance's Dragonite (2013 Japan)
 * "Find Pokemon" Funfest Mission Magneton (2013 Japan)
 * "Find Pokemon" Funfest Mission Dragonair (2013 Japan)
 * "Find Pokemon" Funfest Mission Shelgon (2013 Japan)

Generation VI
The releases of Pokémon Omega Ruby and Alpha Sapphire add new functionality to the White Flute item. When used in an area, it can reduce the level of wild Pokémon by one to four levels, causing some Pokémon to be underleveled. Pokémon listed below that require the White Flute are marked with an asterisk(*) in their obtainable level.

Some special distribution Event Pokémon are underleveled. These are now unavailable through legitimate methods.
 * Ghetsis' Hydreigon (2016 Japan)
 * Mega Evolution Distribution Tyranitar (2014 Japan)
 * Pokémon World Championship Qualifier Gift Tyranitar (2014 Korea)

Friend Safari
The Friend Safari in Pokémon X and Y is an unusual location, in that Pokémon that appear are dependant on registered friend codes within the memory of the Nintendo 3DS console. As a result, not all Pokémon are obtainable to all players without a suitable friend code. All Pokémon found in the Safari are level 30.

Generation VII
Underleveled Pokémon can be found in the Poké Pelago. However, the level and rarity of Pokémon obtained from the Poké Pelago increases as the player's Trainer Card is completed, meaning there is a limited time to obtain the following:
 * Pokémon Sun and Moon
 * Kadabra - at level 11, until completing the Akala Island Grand Trial
 * Drifblim - until completing the Ula'ula Island Grand Trial
 * Pokémon Ultra Sun and Ultra Moon
 * Flaaffy - at level 11, until completing the Akala Island Grand Trial
 * Jynx - until completing the Ula'ula Island Grand Trial

Some special distribution Event Pokémon are underleveled. These are now unavailable through legitimate methods.
 * Original Cap Pikachu (2017)

Trivia

 * Using in-game trades, some first form Pokémon can be obtained at a level lower than possible in the wild
 * Poliwag, Mr. Mime and Farfetch'd in Pokémon Blue Version (Japan)
 * Skitty in Pokémon Ruby and Sapphire Version and Meowth in Pokémon Emerald Version
 * When the Level 50 cap rule is applied in the Battle Spot some Pokémon become underleveled. These are Bisharp, Solgaleo, Lunala, Braviary, Mandibuzz, Dragonite, Tyranitar, Volcarona, and Hydreigon.
 * Illegal underleveled Pokémon can be obtained through cheats and glitches, such as the Mew Glitch in Generation I or the Pomeg Glitch in Generation IV
 * Some underleveled Pokémon are used in the Battle Frontier in Pokémon Emerald Version