As you go off the beaten path or progress deeper into Hoenn, there will be times where you’ll encounter an obstacle than you can’t pass without the aid of Pokémon.
During this moments, you will need to use the corresponding TM (Technical Machine) or HM (Hidden Machine) learned by your Pokémon. TMs and HMs can be found naturally through the course of your journey, although some are easier to find than others.
Beware that once learned, HMs cannot be forgotten (until you reach the Move Deleter later on). This can be especially aannoying if you have a lot of great moves on your Pokémon and you don’t want to ruin their movepool.
For this purpose, some players like to bring along a HM Slave (or two) - a Pokémon whose only purpose is to use HMs. This way, you don’t have to compromise your battle Pokémon, but it means you’ll be wasting one of your six party slots.
This move lets your Pokémon - with sharp claws or a scythe - cut down a thorny plant blocking your way to a secret path or item. In battle, its damage is pretty poor and outside of battle, there are few (if any) thorny plants in the way of progress.
Used to brighten up dark areas, particularly in caves. Not necessary, since even the darkest of caves can still be navigated if you have a good eye, but it helps a lot. In battle it reduces the opponent’s Accuracy; not terribly useful, but it does target adjacent opponents in Double/Triple Battles.
HM06: Rock Smash
Does… exactly what it says, breaking small, cracked rocks in the way. Besides opening up side routes, Rock Smash occasionally lets you encounter wild Pokémon hiding inside the rocks, items or - after acquiring the Eon Flute - even Pokémon fossils (found in Mirage Spots)!
Strength flexes your Pokémon’s muscles, allowing you to move big cubic rocks, provided there is no other obstruction in the way (such as a wall). Cue a variety of Strength-based puzzles, where you must cleverly manoeuvre the rocks, often dropping them into pits, to get exactly where you want.
Once you’ve used Strength once, you will be able to continuously push rocks until you leave the area, so there’s no need to keep applying Strength each time you want to nudge a rock.
TM94: Secret Power
Secret Power is rather unique, allowing you to create entrances in certain suspicious walls, trees or bushes. Now you won’t exactly find anything new beyond - just empty space. However, that space can be remodelled as your own personal Secret Base.
Surf lets you traverse bodies of water, such as rivers, ponds or even the vast seas of Hoenn. While surfing, you may encounter wild, water-based Pokémon. Of all the HMs, Surf is one of the better ones for battle and ideal for your special Water attackers.
This water-based HM allows you to dive where there’s deep water, and resurface where there’s light coming from above. Besides providing access to otherwise inaccessible areas, you can also find Pokémon and hidden items while underwater.
This final HM completes the unholy trinity of water HMs; with this you can ascend and descend the giant waterfalls encountered while using Surf. Like Surf, Waterfall is a powerful move in its own right and a good fit for any physical Water attackers.