TMs and HMs are some of the most important items in the Pokémon series. Technical Machines and Hidden Moves, as they are formally known, were originally introduced in the very first Pokémon games and have been a part of the franchise ever since. These items can be used to teach Pokémon new moves they might not be able to learn through natural level progression. Only certain TMs and HMs will work on certain Pokémon, though, and some Pokémon can't use HMs or TMS at all.
While TMs and HMs serve a similar purpose, they function fairly differently. Technical Machines teach Pokémon moves they can only use in battle, while Hidden Moves can be also used outside of battle, often allowing players to advance the plot in Pokémon games. Normally, when a player reaches a new city or town, there are roadblocks like trees or boulders blocking the path to the next area. Players then have to find an HM and defeat a Gym Leader to gain the ability to use that move outside of combat, letting them get past the roadblocks.
HMs have a history of frustrating players, as they normally aren't the best moves and cannot be removed from a Pokémon's moveset unless taken to the Move Deleter. This is likely why HMs were removed in Pokémon Sword and Shield and replaced with TRs, Technical Records. Technical Machines, on the other hand, are much easier to use, as they can be removed simply by teaching a Pokémon a new move to overwrite the TM. Unlike HMs, though, which can be used an unlimited amount, TMs can only be used once. If players want to use a TM a second time, they'll have to find or purchase a duplicate.
Which Pokémon Can't Use TMs & HMs
While Pokémon that can learn as many HMs as possible are often sought-after for their utility outside of battle, many can't use any of them. Here is a list of every Pokémon that can't learn TMs or HMs in at least one generation of games, compiled by Bulbapedia:
- Beldum
- Blipbug
- Burmy
- Cascoon
- Caterpie
- Combee
- Cosmog
- Cosmoem
- Ditto
- Kakuna
- Kricketot
- Magikarp
- Metapod
- Scatterbug
- Silcoon
- Smeargle
- Tynamo
- Unown
- Weedle
- Wobbuffet
- Wurmple
- Wynaut
There are a number of similarities between these 22 Pokémon. For starters, 12 are Bug-types, famous for being among the weakest Pokémon in the series. While it's still surprising to see them account for more than half of the Pokémon unable to learn TMs and HMs, several of them are cocoon Pokémon, like Metapod and Silcoon, which tend to only learn defensive moves like Harden.
Two of the more interesting names on this list are Smeargle and Ditto. Ditto can transform into any Pokémon it sees with its Hidden Ability, Imposter, and the move Transform. This allows Ditto to copy any Pokémon's moveset, thus giving it the ability to use any move. Meanwhile, Smeargle has the ability Sketch, which permanently copies the last move used by an opponent. Ironically, despite being able to use almost every move in the entire game, neither Ditto nor Smeargle can learn moves through TMs or HMs.
Two Legendary Pokémon, Cosmog and Cosmoem, even made the list, as well. Whether because of their inability to learn TMs and HMs or not, many of these Pokémon - while they may be adorable - aren't all that good, so trainers are best advised to avoid them, if possible.
Source: Bulbapedia