A Mii Fighter Costume modeled after a Slime was made available as DLC for Super Smash Bros. Ultimate. They also make a cameo appearance in the background of Yggdrasil's Altar, which is a part of Fighters Pass Volume 2.
Slimes are a race of creatures with a squishy body that resembles a water droplet. According to series creator Yuji Horii, they were originally meant to be more unappealing and ugly with a much more moldy appearance akin to other RPG monsters; however, artist Akira Toriyama decided to go against the trope as he felt he should make Slimes more endearing.
Much like Goombas in the Super Mario series, Slimes are the first enemies the Hero encounters in the Dragon Quest series. They are the weakest enemies in the series as they lack any real offensive abilities and are easily defeated in a single strike. More recent titles have given certain Slimes personality and their own language, which consist of slime-related puns such as "gooman" or saying "slurp" or "goo" as a verbal tic. Some have also become travel companions for Heroes, with them being known as Friendly Slimes.
Due to their simplistic design and increased popularity, multiple Slime variations have appeared throughout the series, eventually forming the Slime family. These have included She-Slime, Liquid Metal Slime, Healslime, and King Slime. Their popularity has also earned them dedicated spin-off titles such as Dragon Quest Heroes: Rocket Slime, as well as playable appearances in other games like Itadaki Street and Mario Sports Mix.
DLC Spirits of a Slime, King Slime, and a Liquid Metal Slime were added into the game as a part of the DLC Spirit Board in Hero's Challenger Pack.
The standard Slime is a Grab Spirit under the Novice class. Its Spirit Battle uses a blue 5-man Kirby Team, as both have squishy bodies. It is a Stamina match and all Kirby opponents will only perform Neutral Aerial Attacks, a reference to a Slime's basic attack being a jump-based strike. Once the Kirby Team has been disposed of, a lone giant Kirby will appear, who is meant to be a stand-in for King Slime. The stage is the Battlefield Form of Gaur Plain, meant to resemble the grassy areas that Slimes often inhabit, with the song "Fighting Spirits - DRAGON QUEST III" playing in the background. All opponents must be defeated to win. If the Spirit is maxed out to Level 99, it will be enhanced into King Slime, as in Dragon Quest it is formed after several single Slimes are combined.
The Liquid Metal Slime is a Support Spirit also under the Novice class. Its Spirit Battle also uses a blue Kirby, though is now fittingly Metal. He is equipped with a Franklin Badge, a reference to its resistance to magic spells, and has super armor. It is also a Stamina match, though only lasts for 30 seconds, which is meant to mimic its tendency to flee from the player when spotted. The stage is the Battlefield Form of The Great Cave Offensive, as Liquid Metal Slimes are commonly found in caves, with the song "Battle for the Glory - DRAGON QUEST IV" playing in the background.
Both a Slime and, more rarely, a Liquid Metal Slime have a chance of appearing in the background of Yggdrasil's Altar at anytime during a match.
A Slime also appears as a part of Hero's Down Taunt and in one of his victory screens. Solo, the Hero from Dragon Quest IV, wears a Slime earring, which turns into a Metal Slime in his alternate palette swap.
Two Slimes make a cameo appearance in the Heroes' reveal trailer. In it, they are briefly seen reacting to The Luminary being launched and then fleeing.
According to both Masahiro Sakurai and Dragon Quest creator Yuji Horii, the development team briefly considered Slime to be the chosen fighter to represent the series, but had to be scrapped after realizing its limited moveset potential. Though Sakurai preferred the Hero, he has stated he would not have opposed Slime being chosen instead if Square Enix had requested it.
- Slime's appearance in Smash marks the third time it has appeared alongside Mario and Final Fantasy characters, following the Itadaki Street series and Mario Sports Mix.
- Slime's segment of the "Mii Fighter Costumes - Round 2" trailer make several references to the Dragon Quest series:
- Captain Falcon performs one of his Taunts at the Mii Gunner, which involves performing a beckoning gesture. This is a possible reference to Dragon Quest V, where monsters can join the Hero's party after defeating them.
- The Mii Gunner is later seen, now in Metal and running away from The Luminary; it is a reference to Liquid Metal Slimes and their tendency to run away. The Luminary is also seen performing Hatchet Man, which is often used to defeat Metal Slimes as it has a high chance of dealing a critical hit.
- The Slime hat is one of three headgear pieces to have special physics, the other two being the Lloyd and the Nakoruru wigs.