Let's talk about Pikachu.
Pikachu has fairly modest base stats, but a terrific movepool. According to one of its Pokedex entries, "When it releases pent-up energy in a burst, the electric power is equal to a lightning bolt." This is fitting, as two of Pikachu's most potent attacks are called "Thunderbolt" and "Thunder." In addition, Pikachu (along with its evolutionary family) is the only Pokemon capable of learning the extremely powerful attack Volt Tackle, which causes damage to the user as well as the target. All three of these attacks have a chance of paralyzing the target, which reduces their speed by 75% and sometimes renders them completely immobile.
Pikachu can also have the ability Static, which has a 30% chance of paralyzing any opponent who makes contact with it. The alternative to this ability is Lightning Rod, which absorbs electricity-based attacks, rendering them entirely ineffective on Pikachu and in fact boosting his special attack power by 50% with each attack absorbed. A Pikachu with Lightning Rod would make an extremely entertaining opponent for Cole MacGrath! Each could pelt the other with electric attacks of catastrophic power without end, neither making any progress and both actually powering up their opponent. Thankfully, Cole has Ice- or Fire-based attacks he can fall back on, and Pikachu can learn a handful of strong attacks of other types, such as the Steel-type Iron Tail.
But wait, there's more. When holding a Light Ball, a special item even wild Pikachu are sometimes found carrying, Pikachu's attack stats are doubled. Those Thunder strikes will pack quite a punch now, to say nothing of Volt Tackle.
And in case you think you can outspeed Pikachu, well, maybe you're right. Pikachu's base speed is a respectable 90, on-par with Lucario's. However, Pikachu learns the useful psychic move Agility. A single use of this doubles its speed, while it can use the move up to three times to quadruple its base speed. I doubt that will be necessary, though, as merely doubling its speed makes Pikachu faster than the fastest Pokemon to date, Deoxys in its Speed Forme. For reference, Ninjask, a 2-foot-tall, 25-pound flying bug that is a bit slower than Deoxys in Speed Forme, is said to fly so fast that it is invisible to the naked eye.
So, to recap: With a single setup move, Pikachu is so fast it is invisible. It can strike from afar with (double) the power of a lightning bolt, or get in close with a strong melee attack. It can cripple its opponents' speed or even render them immobile with most of its attacks. It is immune to electric attacks and absorbs them to grow more powerful (why hello there Zeus, you're looking a little bit nervous).
Pikachu is Samus-tier broken. And it's so relatively weak compared to other Pokemon (*cough* Lucario) that it's not even considered competitively viable. But competitively viable and canonically powerful don't necessarily go hand-in-hand. If we take a look at what Pikachu has managed to accomplish in any of its non-video game appearances, it has an impressive resume which includes taking down several legendary (essentially demi-godly) Pokemon.
I felt compelled to write this bit up because I suddenly really thought about Pikachu and realized that it was being grossly underappreciated here. Most people look at it and see a cute little stuffed animal, which is exactly what Nintendo wants you to see. But in actuality, Pikachu could fully incapacitate most characters on either of these rosters at the speed of light. ...There wouldn't be much left of them, either.
