This is an auto-chargeable special move that fires a long ranged electric projectile. Like most moves of its nature, the move will automatically charge once the B button is tapped, and pressing the button will fire it during the said period. Also during said charging period, the move's charge can be stored by shielding or rolling (the latter done by tapping left or right). In midair, charging can be cancelled with an air dodge. Any stored charge is lost if Robin flinches from a hit while charging or is KO'd.
Charging or using this move changes Robin's active tome to Thunder. The tome has a limited amount of durability, which is expended when the attack is released, and when depleted causes the tome to be automatically discarded. The discarded tome acts as a projectile that will damage opponents as it falls, and which can be caught and thrown like an item. After it breaks, a cooldown of 10 seconds passes before the tome is replaced and Thunder can be used again.
If Kirby copies this move and exhausts the Thunder tome that he acquires from inhaling Robin, the copy ability is instantly discarded (with Kirby immediately losing Robin's "hair" hat without any visual indication), and any projectile it produced will prematurely disappear.
Trying to use the move while the tome is broken before replacement will have Robin perform the animation for the cast, but only a small puff of smoke will come out with no effect whatsoever.
Thunder has 4 different stages, each with different projectile properties, damage and knockback that is determined by the charge of the attack. Depending on what stage the attack is, the durability points used varies. A total of 20 durability points can be used before the tome breaks. When Elthunder is charged, the tome will flash yellow. When Arcthunder is charged, the tome will glow red. When Thoron is charged, Robin will put the tome away and launch the attack when B is pressed again.
All stages of the move (excluding Thoron) can miss smaller characters while they are crouching or dodging, as they travel a distance above the floor.
If the special attack button is held when casting Thoron, the beam will extend faster and deal more damage compared to if the button were simply tapped.
Special Move customization was added in Super Smash Bros. 4. These are the variations:
Thunder magic is one of the most commonly recurring types of offensive magic in the Fire Emblem series, and is one of the five categories of offensive magic, along with fire, wind, light, and dark. Thunder magic is commonly grouped with fire and wind into the collective school of anima magic, or the magic of nature.
In Fire Emblem, each class is restricted in what weapons they can use by how proficient they are in that weapon type. In many games, the anima magic categories organize their spells into a series of stages, with each spell being more powerful than the last and requiring more weapon experience to use, and the thunder spells used by Robin in Smash are taken from these stages. While Fire Emblem does not have a charging mechanic for spells like Smash does for Thunder, it could be taken as a reference to weapon experience.
In Fire Emblem Awakening, Robin's starting inventory in the main game features a Thunder tome, and begins the Premonition chapter at the beginning of the game with a Thoron tome. In Fire Emblem Fates, Thoron is a special weapon which can only be used by Robin as bonus amiibo content.