There is only one answer to this question.
Octillery is fucking badass. Let me ask you this; can your Pokemon spit fire? Can your Pokemon shoot water? Can your Pokemon fire a concentrated beam of ice? Can your Pokemon melt the brains of its foes through the sheer power of its mind? Octillery does all of those things. If there is a beam based attack, Octillery will learn it. Why? Because it's an octopus canon, one of the most implausible yet ridiculously awesome combinations imaginable. Octillery says fuck you to the laws of physics and does whatever the fuck it wants. It's that awesome. Your petty logic has no effect on him. How can a fish evolve into an onctopus? Who gives a shit, it's fucking Octillery.
So yeah, I'd like an Octillery.