Ok. First off, all the moves mentioned, if known how to be treated properly, are a weak part of pikas game and render any spammer of those moves useless. The only garuanteed pika aerial combo i am aware of is uair -> to any other aerial. anything beyond that can be escaped from. Dsmash? I am sick and tired of hearing how broken it is. Perhaps it is because i have faced too many people that it has little effect on other then refreshing moves. Smash DI with both sticks straight up gets you out of the dsmash very quickly. offline it can be done in as quickly as 2 hits. I should know, i play a falco who does that every time. I will say even when DI'd out of, pikachu can play a sorta tech chase, but he loses more often then not. also aerials of pikachu have mediocre to poor priority, mediocre to poor range, and light damage and knockback other then nair and maybe dair.if a pika spams it at you, shield grab. it really is that simple to stop sadly. but yeah, such a pikachu doesnt sound scary at all.
Wait Thunder? ok thunder in the right hands can be devastating. even then, it can be quite obvious when thunder is used. you should really only fear thunder if you are off the edge or if you get knocked into the air. it is far more powerful online. I <3 thunder.