At my local tournament scene, I use Pikachu alongside Ness, and while I've become pretty exceptional with Ness, I can't help but struggle while using Pikachu. Everyone tells me, "In order to succeed with Pikachu, you have to be aggressive. You gotta be in their face!" So I try that, but I only get punished. It makes me feel like I've always got to approach, which can get really punishable. So can my fellow Pika mains help me out? Go over approaches, quick attack, etc.? And is being a bit more defensive even bad with Pikachu? How can I play smart while also being aggressive? (with the new shieldstun changes, this is especially important)
The big thing here is that "being aggressive" isn't the same as "always approaching." A lot of Pikachu's strength centers around how unpredictable and explosive he can be when he gets in, but you can't be too hungry with him or you'll just get bopped. When I play Pikachu, I spend a lot of time floating around just outside of my opponent's range, while zipping around with Quick Attack and whiffing Fairs, Dairs, and RAR Uairs and Bairs. I also perform SH Fair FF's such that they completely whiff, but I'm in range for a Dtilt, and SH Fair / Dair AC out of shield grab range, but in range for a Ftilt or whatever. The idea is that you want to remain safe while threatening that you can come in at any time--you want it so that your opponent can't call out in advance whether any random Pika short-hopped aerial is just another footsie whiff, or if you're making an attempt to hit them, and you want make sure they never know whether any given Quick Attack is an approach attempt, a cross-up attempt, an escape, or a bait.
I liken Pikachu play to Abel from Street Fighter IV or Sol Badguy from Guilty Gear: While they're both considered "aggressive characters," you have to spend a lot of time floating just outside of your opponent's comfort range and pressing buttons from a safe distance, so that when you
actually go in, they don't automatically react with the one magic button that beats you (Shield Grab in Pikachu's case).
In short: Practice your "non-approach," where you get
frustratingly close to your opponent with your Fairs and QAs. This will do one of two things: either they will start pressing buttons because they want to punish your approach, except they'll whiff and you'll punish them with Ftilt / Dtilt / Fsmash / Dash Attack / Dash Grab, or they'll start to notice that not every Pika-pproach is actually landing into them, in which case they now have to do the extra mental math of "will he or won't he get in range?" which leads to
hesitation and which allows you to actually challenge their shield with your aerials without being punished every single time.