Mega Man Legends is one of the many sub-series in the Mega Man series. It is, chronologically, the last of the series. Despite there only being 4 mainstream games (Legends 1-3 and Misadventures of Tron Bonne), it is one of the more popular Mega Man sub-series, rivaling the likes of Mega Man X.
In Super Smash Bros. Battle Royale, the Legends franchise has a lot of material. The biggest being Tron Bonne as a playable character. Legends gets more references in Battle Royale than the Classics and X games, just like a Capcom Versus game would.
Mega Man Legends (game)
The Mega Man in this series is Mega Man Volnutt, a "digger" who searches ruins for gems called Refractors, which are used for many things (running a ship, sell for money, etc). He is aided by Roll Caskett (a very smart girl who knows how to work machines and make tons of weapons), Data (a monkey who can save your game and heal you), and Barrel Caskett (an older man who accompanies the group).
In the first Mega Man Legends game, the group crashes on an island known as Kattelox Island after their ship, The Flutter, breaks down. Volnutt and the group go to the city, hoping to find help. Soon after, Volnutt encounter the Bonne Family, a group of pirates who raid villages to make money. At Kattelox, Volnutt encounters Tron Bonne (a girl around Roll's age who (debatably) is even smarter, is afraid of dogs), some Servbots (cute little lego-men who follow Tron's every command), and Bon Bonne (a baby who can only utter the phrase "Ba-Boo!"). After defeating each of them, Volnutt obtains a digger's license, allowing him to go into any ruin in search of money, refractors, etc. Soon after, he runs into the final member of the Bonne family, Teisel Bonne (a crazy (yet awesome) male with great leadership, very close with his family, the tactician of the family).
In Battle Royale
This game is the prime focus of the Legends representation in Battle Royale. Tron Bonne originated in this game, as did Mega Man Volnutt, Roll Caskett, Servbot, Teisel, and Data. The Gesellchaft was in this game, but it's use in Battle Royale was seen in the prequel to this game, The Misadventures of Tron Bonne.
The Misadventures of Tron Bonne
This game is a prequel to Mega Man Legends. The game's ending actually leads right into said game. After searching through some ruins for money, Teisel Bonne is encountered by a man named Glyde. He tells him that "his loan to Lex Loath needs to be paid. NOW.". Teisel begs him for more time, but Glyde refuses. He defeats Teisel in combat and takes him and Bon away.
Meanwhile, back on The Gesselchaft, Tron gets worried about Teisel and goes to search for him. When she arrives at the scene, she sees a group of Servbots, who explain to her that Teisel and Bon were taken away. After returning to the Gesselchaft, Tron gets some Servbots to find a bill that Teisel had paid. In it, Teisel had said that he owed Lex Loath 1 million Zenny.
Tron: … What?!? 1 million zenny?!?
Tron then decides to get the money back herself and save Teisel and Bon.
In Battle Royale
A small part of this game is in Battle Royale. The Gesellchaft Stage is based off of the Gesselchaft from this game. The idea of Tron's favorite Servbot originated from this game, as well.