A Rathalos (リオレウス, Liolaeus) is a type of flying wyvern from the Monster Hunter series, created by Capcom. They are one of the most well-known monsters in the series, and can appear in many varied habitats.
A Rathalos is a recurring monster from the Monster Hunter series, and is both the flagship monster for the original Monster Hunter and the de facto mascot of the series as a whole. While many monsters of varying types are referred to as "Wyverns" in the Monster Hunter universe, the Rathalos closely fits the real-world classical definition of a wyvern, as an armless, winged dragon with fire breath and poisonous claws. It is sometimes known by its epithet "King of the Skies", and belongs to the Flying Wyvern family of monsters. In addition to its female counterpart Rathian, there are a number of Rathalos subspecies in existence, such as Azure Rathalos. Its description in Monster Hunter World states that "Rathalos descends upon invaders from the sky, attacking with poison claws and fiery breath", which is reflected accordingly in its attacks in Smash.
Armor, in both Blademaster and Gunner variants, can be created from materials procured from hunting Rathalos in its home series.
Much like Charizard, Rathalos is not explicitly referred to as a dragon in its home series, but is treated as one in Super Smash Bros. Ultimate. This discrepancy is mostly due to the Western localization of Monster Hunter, as Flying Wyverns (such as Rathalos) are referred to as 飛竜種 ("flying dragon species") in the original Japanese, while Elder Dragon boss monsters simply use a different, antiquated kanji for "dragon" (古龍種, "old dragon species"). The Rathalos is also weak to Dragon elemental attacks, a trait possessed only by Elder Dragons and dragonlike wyverns. Spinoffs such as a crossover with Puzzle and Dragons make it clear that Rathalos and many other wyverns are considered to be dragons outside of the taxonomy used in their home universe.
As a costume
Armor created with Rathalos materials from Monster Hunter, called the Rathalos Blademaster Armor, appeared as a downloadable content costume for Mii Swordfighters. The armor's design is derived from Monster Hunter Tri and later entries in the series, excluding Monster Hunter: World.
As a Boss
The boss Rathalos fights like he did in his home series. He fights using his talons, tail swipes, fireballs, and flying into the background, and can stun his enemies with a screeching roar. During the fight, certain items will appear, such as Explosive Barrels, Deku Nuts and Pitfalls. The Rathalos is vulnerable to all of the mentioned items, which will open him up to free damage before he recovers. The Rathalos can also be stunned briefly by breaking the armour on either his face or back, triggered by dealing sufficient damage to that area first. Attacking his tail will cause him to drop an item, a reference to how his tail can be severed for extra items in his home series.
When his Stamina drops to 0, the Rathalos will drop the ground and flail around before lying still, as in his death animation in the Monster Hunter series.
The Fighters that are assigned to fight Rathalos in Classic Mode at the end of their round are Yoshi, Marth, Duck Hunt and Piranha Plant. Bowser and Hero are also assigned to fight Rathalos, but are not the final round. Bowser fights Mario afterwards, then Metal Mario (upon Mario's defeat), while Hero has two more regular rounds before fighting Robin, then a giant Charizard (upon Robin's defeat). Usually, Roar/Rathalos plays during the battle, but when Hero fights Rathalos, Fighting Spirits - DRAGON QUEST III plays, and Galeem/Dharkon during the boss rush.
There are nine main attacks that Rathalos uses in his boss battle:
World of Light
Rathalos is encountered in the Forest Hill sub base found on Tortimer Island (possibly due to his kind appearing in forests in his home series), where the player can see him as soon as they enter this sub base. The player must chase Rathalos around the sub base area until they eventually corner the boss by approaching him from behind, which leads to the battle. Defeating Rathalos is necessary to weaken the shield protecting Galeem. He is later fought again in the true final during the second phase, where the player must fight every boss except Master Hand and Crazy Hand. He's the last of the Light Realm bosses to appear onscreen during this phase, which could indicate that he's the third boss in the game.
As an Assist Trophy
Upon being pulled from an Assist Trophy, a Rathalos is summoned by flying down from the sky and begins to attack his summoner's opponents. He uses the same attacks as the boss version, but he does not fly into the background for any attacks. Additionally, he is immune to Explosive Barrels, Deku Nuts and Pitfalls. He can be KO'd for a point, though he is very durable, has flinch resistance, and cannot be grabbed.