Riolu in depth
An aura puppy with a canine mask
Riolu's design is based on a canine-looking animal, with features reminiscent of a jackal and, because of its facial markings and ears, also of a small masked canine. The association with Anubis fits its connection with aura: it does not merely emit energy, but uses it as a language and as a detector of emotions.
The Japanese name, リオル (Riolu), is a partial anagram of ルカリオ (Lucario), with the central syllables missing. The link between the two names reinforces the idea that Riolu is Lucario's younger form, even though its behaviour is not simply that of a smaller version of its evolution. Pokédex entries stress that it is still a baby, even when it already displays unusually high physical stamina.
The evolution that changes its role
Riolu appeared in Generation IV as Lucario's pre-evolution. Its evolution does not depend on a stone or a specific move: it needs friendship and must gain the level during the day. This ties the moment of evolution to the way it is treated, which fits a species that perceives the emotions of humans and Pokémon.
Over the generations, its mechanical role gained an additional option through Prankster as a Hidden Ability. This Ability does not directly increase damage, but changes the order of status moves and gives value to actions such as Swords Dance, Helping Hand, Protect or Copycat. It also underwent the defensive change associated with the arrival of the Fairy type, which added a weakness to its Fighting-type profile.
What it offers before becoming Lucario
Its Attack of 70 is enough to make use of moves such as Close Combat, Force Palm or Earthquake. Its Speed of 60 lets it act before certain slower opponents, but does not make up for a Defense of 40, a Special Defense of 40 and HP of 40. Taking a powerful neutral hit will often leave it unable to battle, so it should not be sent out without a clear prediction.
In Little Cup, its defining trait is the combination of Prankster and Copycat. Swords Dance can prepare a physical attack, while Copycat lets it repeat the last move used. This idea requires control over the order of actions and avoiding situations where the opponent gives it a useless move to copy. Against teams with Ghost-type Pokémon, Fighting-type attacks lose value, so Crunch or Shadow Claw help keep it from being completely walled by them.
A youngster with direct competitors
Mienfoo and Timburr compete with it on Little Cup teams because they offer a more consistent physical presence. Riolu responds with broader coverage and the ability to use status moves with priority thanks to Prankster, but pays for that flexibility with poor defenses.
In a playthrough, its best period comes before evolving, when it can use Ice Punch, Thunder Punch, Metal Claw and Earthquake to cover threats that a pure Fighting type could not pressure. Once it fulfils the friendship condition, Lucario takes its place and completely changes the stat spread and battle options. The difference between the two stages is not just visual: Riolu fights as a fast, fragile youngster, while its evolution already belongs to an entirely different tier of use.