Pokémon

It's Sonic the Hedgehog, Pokemon style.

@AgentJ said:

" @Obsidian609 said:

" @AgentJ: That or it could be a new evolution for Riolu. "

They've only had multiple evolutions for the same pokemon all of what, twice? Three times? (lets see, Politoad, Belossum, Eevee) Considering its size, Lucario seems more plausible to me. "  

Not true branched evolution, while not common has occured at least 10 times. (11 if you count recieving a Shedinja when Nincada evolves into Ninjask while an empty slot is open in your party and the player has an empty Poke ball) 
 
The pokemon that have branched evolution are: 
 

• Gloom
• Poliwhirl
• Slowpoke
• Eevee
• Tyrogue
• Wurmple
• Kirlia
• Snorunt
• Clamperl
• Burmy

 
and Nincada if you count the Shedinja bit. 
 
Three of these 10 being new ones that were added in 4th gen (Kirlia, Snorunt and Burmy[who was introduced in 4th gen]) along with Eevee obtaining two new evolutions.

@AgentJ:
Yes but these 10 (technically 11) were added over the course of 3 generations* (2,3,4) meaning that there has been on average three new branched evolutions added each generation starting with the second. In reality the new ones have actually been four branched in 2nd, two branched in 3rd[technically three], three branched in 4th and total branched would raise the 2nd and 4th by 1 to five and four respectfully. 
 
Meaning that it is highly likely there will be pokemon with branched evolution in generation 5. So I wouldn't discount the possibilty that they would give Riolu one, especially given Lucario has become one of the iconic pokemon they have given a large role to in the films and developed quite a bit of mythology behind making it unlikely they would give Lucario a new evolution.
  
Also if it is to go with the whole dark Ash thing the OP elluded to than it wouldn't make sense with Lucario as his evolution is by having a Riolu with maximum happiness level up.  
 
Having Riolu evolve via a stone, item hold or trade with item would make sense if they associated the object with darkness (ie. a dusk stone) or something similar. This is of course assuming it is related to dark Ash.

*Eevee being the notable exception of being the first branched evolution in the first game and the 5 and 4 in both 2nd and 4th refer to the two new Eevee evolutions each added. Which would technically mean 9[10] in generations following the first.
 

@Kelleth: They certainly look to be filling the Canidae pokemon archetype.

@John_Martone:

Yep Slowking was added in Gold/Silver. Instead of letting Slowpoke evolve into Slowbro via leveling you trade the Slowpoke while (s)he is holding a King's Rock. Slowking itself looks kind of like Slowbro except with the Shelder on his head instead of tail, which apparently has the effect of greatly increasing the intelligence of Slowking. (Get thyself to a Pokedex.)  
 
Also they have added a new evolution method each generation. Although the 3rd gen was peculiar for introducing two new and very strange evolution methods and each only applied to one particular pokemon. Being the extremely rare Feebas's evolution into Milotic by having a beauty stat over 170 and than leveling and Nincada evolving into Ninjask via level up and provided the player has an open pokemon slot (on them not in the PC) and a spare Poke ball (any type will do) Shedinja as well. 
 
So I suspect there will probably be some new kind of evolution method here as well.