When using Rock Smash, Charizard takes a large rock and headbutts it, shattering it into many pieces in the process. When Charizard headbutts the rock, it deals high damage and knockback, while the fragments deal much lower damage and knockback, but they can hit multiple times to build on extra damage.
In Super Smash Bros. Brawl, the head butt deals a rather impressive 18% damage, along with strong vertical knockback, making it a great KO option. After the rock has shattered, the rock shatters into five smaller pieces that fly forward in a spread effect, dealing 5% damage each. The fragments are considered to be a projectile, so they can be reflected (although they cannot be absorbed). If the headbutt and all rock fragments hit, it will deal a massive 43%, though this can only occur in normal matches when Rock Smash is landed point blank on a low-damage opponent. However, against bosses, Rock Smash is an extremely effective move, as their massive size and inability to flinch ensures they will always get hit by all the rock fragments when hit with Rock Smash; this is so effective that Charizard can defeat all bosses faster than any other character in Brawl, and holds the world record time in Boss Battles, even on Intense difficulty (barring Peach with stitch-face turnips, which requires extreme luck to pull multiple stitch-faces across every Boss Battle and incredibly precise, tool-assisted inputs). Rock Smash's massive damage potential also means it is one of the few moves that can break a full health Smash Ball in one hit.
Rock Smash is easily considered to be one of Charizard's best moves in Brawl, as it is a damaging and powerful KO move which can be used on both the ground and in the air. The fragments can also build on some extra damage and they give the move solid shield pressuring potential, draining shield damage, easily shield poking and generally making the move difficult to punish. Even if the opponent hits Charizard before it headbutts the rock, the fragments can prematurely break early, building up damage on the opponent (allow Charizard must be hit in its upper body and the opponent must naturally be in front of Charizard). This can occur as early as frame 1 of Rock Smash's animation, allowing it to be used as a very quick, defensive damage racking tool. Because of these factors, Rock Smash is a excellent move, being a great approach tool, pressure tool, defensive tool and it is all around a great move to rack damage or to score KOes. It is one of Charizard's most useful moves as a result.
In Super Smash Bros. 4, Rock Smash has now become Charizard's down special (replacing Pokémon Change due to Charizard becoming a solo character), as Flare Blitz has become its new side special. Besides the move being remapped, it has seen some changes.
One positive change the move received is that it now has super armor throughout most of startup. This allows the move to tank through attacks and hard punish them more consistently.
However, Rock Smash has mostly seen negative changes which hinder the move overall. The headbutt now deals a less impressive 14%, noticeably reducing its knockback and subsequently making it a worse KO move overall. The fragments now also only deal 3% each, making the move only deal 29% total in the rare instance where all hits connect.
In addition to this, the fragments can no longer prematurely break if Charizard is hit out of the move early. This means that the move having super armor is essentially a trade off. On the one hand, it is more consistent (being able to fully protect Charizard against all attacks from any angle, which the fragments could not do) and it can lead into a stronger punish. On the other hand, this makes the super armor less safe against low lag attacks, as players can now hit Charizard during its armor frames and potentially shield/dodge the rest of the attack, as opposed to instantly getting hit by the fragments, while Charizard receives potentially minimal lag depending on the strength of the attack. Along with this, the super armor does not start until frame 5 (as opposed to the fragments, which were a frame 1 option), making it a slower defensive option.
The move also has smaller hitboxes, along with having 10 more frames of ending lag, making it a more punishable move overall. Because of these changes, Rock Smash is a less effective move overall, although it still remains a solid tool in Charizard's moveset.
Due to Charizard becoming part of the Pokémon Trainer's team again in Super Smash Bros. Ultimate, Pokémon Change replaced Rock Smash as its down special move, with Charizard retaining Flare Blitz as its side special.
Special Move customization was added in Super Smash Bros. 4. These are the variations:
Rock Smash, introduced in Generation II, is a physical Fighting-type attack in the Pokémon games. It has alternated between TM and HM status over time. In battle, it is a generally weak move with a 50% chance of lowering the target's defense; it can also be used to destroy rocks outside of battle, making it essential in completing many Pokémon games by clearing obstacles to the player's progression.
Charizard can learn Rock Smash by TM or HM in all games since the move's introduction.
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