Pikachu has a pretty high skill ceiling so he's not the easiest to master. Playing him requires a bit of active thinking, since he has a lot of options but some of them can be situational. His play-style can be pretty Match-Up dependent as well. He also requires decently fast (but not that fast) fingers to control. Despite requiring a bit of effort, once mastered Pikachu is an extremely potent character.
As for how to play Pikachu, try to get the hang of using Quick Attack Cancel. The more useful ones are, IMO:
-Short-Hop, Up-B diagonally down.
-Short-Hop, Up-B forward then diagonally down. Covers a lot of distance.
-Up-B diagonally up forward, then diagonally down forward.
-Up-B diagonally up forward, then diagonally down backward. Doesn't really cover much distance but can get your opponent nervous.
-Short-Hop, Up-B straight down. Doesn't really cover much distance but can get your opponent nervous.
-A bunch of other ones. You can get pretty creative with these.

During the slide after you land, you can do whatever. Attack, Shield-bait, do another Up-B, and so on.
You can also try to Combo D-Tilt into U-Smash to KO, but it doesn't work for all Percentages on all characters.

A few things to add:
-Nair to edgeguard if they are behind you
-Uair spike for edgeguarding if they are in front of you
-Thunder edgeguard, if timed and spaced well, cannot be avoided by a large portion of the cast. DO it near the ledge, where they could get hit by the explosion hitbox. If they hit you with their up-b or aerial, they lightning will go through Pika and spike them, or Pika's explosion will kill them.
-Dair is stupidly ridiculous right now. Just running jump offstage with dair and you can kill pretty much everyone lol

Exactly how important is QAC? I use it sometimes but usually only when returning to the stage. Probably should use it more but...I don't know.
EDIT: Read: Just started playing Pika in the new version today.

Why do so many people think that Pikachu is OP?

I'm not denying that he's really good or that he's not upper tier, but I just don't see how he's Top 5.

Can someone explain what makes Pikachu so good outside of his great priority, smash attacks, and, of course, thunder?

Haha lol thats like saying "What makes Falcon's combo game good besides the uairs that link into eachother and Knee?" or "What makes MK so good besides his speed and disjoints?" lol

I don't think he's OP, but he has one of the stronger edgeguarding games. He also has a pretty good recovery, as well as the untapped potential in Quick Attack Canceling. Dair is also really silly with how much knockback and priority it has lolz.

I only said not to use those things cause I already now that they are really good aspect of Pika.

I just want an overall run down on what makes him top 3 in many peoples eye, so please ignore the previous statement .

What makes him good is that he has disjoints when need be, great kill power, good edgeguarding, a great recovery, amazing priority, a generally fast moveset, excellent mobility, and decent damage output.

https://www.youtube.com/watch?v=k_Gnyla ... e=youtu.be
Pikachu can wavedash
redefining the Pikachu meta

That's a Quick-attack Cancel. http://www.ssbwiki.com/Quick_Attack_cancel

Anyone got any better pika kills than this?

PIKACHU NOOO
WHY
I LOVED YOU
WHY DID YOU COMMIT MURDER + SUICIDE

I've got a 0-death, but its not as hype as that one lol

can pikachu suplex people yet

yes he does it with his back throw

pls let utilt have a little bit more knockback or something so that you can't chain utilt most characters from like 0 to like 40-50% (even with proper di)
and bring back the good oil and glorious thunder mechanic from 9a, it has been fun but it's time to get rid of this complete s*** move lmao

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cute