Nintendo eShop
The Nintendo eShop (ニンテンドーeショップ, Nintendo eShop) is Nintendo's primary service for purchasing digital games, serving as a successor to both the Wii Shop Channel and DSi Shop. Beginning with the Nintendo 3DS and continuing onto the Wii U and Nintendo Switch, players can go onto the eShop with an internet connection and download digital titles, and sometimes content exclusive to the eShop (such as download-only titles, and non-video game media like animations). Players can also buy older games from Nintendo's previous consoles on the Wii U and 3DS's Shops.
In the Super Smash Bros. series
Super Smash Bros. 4
Being on the eShop's introductory consoles, both versions of Super Smash Bros. 4 are available to download for their respective consoles, the Nintendo 3DS and Wii U. There also exists a demo for Super Smash Bros. for Nintendo 3DS available to download for free, featuring access to Mario, Link, Pikachu, Villager, and Mega Man and a choice between regular and Ω Battlefield, with the former having items turned on and the latter having items turned off. Super Smash Bros. for Wii U lacks a downloadable demo.
The eShop is also connected to the downloadable content for the game; the 3DS version has a built-in eShop (likely due to the 3DS's modest processing power), while the Wii U accesses the eShop directly. In either version, the player can use the eShop to download characters, stages, or Mii Fighter costumes.
Super Smash Bros. Ultimate
Super Smash Bros. Ultimate is also available for download on the Nintendo Switch. Two versions of the downloadable game exist; one that pays for the game in full, and one that pays for the game and the Fighter Pass, with the price appropriately changing. The Fighter Pass is available for separate purchase, as is each individual fighter. Ultimate also has an eShop menu within it (that accesses the eShop directly, much like Super Smash Bros. for Wii U) where players can purchase the downloadable content for the game (such as the aforementioned Fighter Pass).
Players also can earn Gold Points for Nintendo's My Nintendo service; up until January 31st, 2019, if this process was followed with Ultimate, players would also receive a code to download Piranha Plant for free upon its release. Shortly after the release of Piranha Plant, it was available for purchase on the eShop for those who did not get the Gold Points.