Well, you asked for it m8 have a wall
nair isnt terrible if you hit, its just terrible if you miss, so it has its uses if you follow your heart.
I play pika on a very casually serious level in 4glory, this is what i do
approaching mostly consists of using full jump neutral b and then i run in with my lightning, and go for a grab, roll read or aerial. The electricity just makes approaching a lot safer considering how punishable plenty of pikachu's attacks are.
Another way of approaching is to be defensive in an aggressive way, like running up and shield, staying kinda close but just enough that you could avoid an attack, and then punishing if they do something. I think brawl pikachu plays like this? (I might be totally wrong i don't play brawl) You can also just suddenly do an attack or grab while doing this, and the other person may not react in time. Pikachu's pretty quick.
Now that you have the opportunity to hit them, next you want to put them above you, plenty of characters don't have an effective way to get down to the ground aside from air dodging and double jumping. Through the power of reading an air dodge or a double jump you can keep them up there and continue to rack up %, usually not for very long though since its hard and you only get 6~10 % per read. Any aerial is good for hitting them aside from F-air, I've had many experiences of them suddenly flying towards the ground & escaping after the first hit, then punish me as I fall back down. If they're above you you can also do the cool new thunder thing where you spike them towards you for damage.
The best ways of getting them up there is up smash, down/up throw, dash attack at higher %'s and up air.
Now that you've built all that damage your next course of action is killing them. This can be really hard sometimes. F-smash is an alright move, with the long, disjointed hitbox. It takes a while to come out though so its not really reliable. Up-smash is quick and powerful but short ranged. Both kill at 110~. getting them off stage and edgeguarding with a downair is another way to kill. The most notable ways to get them off stage are dash attacks and back throws. Thunder and d-smash don't really knock back much. There are 3 main ways of landing killing moves
1. praying it works: pretty much just run up and upsmash or hope they run into the f-smash
2. reading a roll/spot dodge. Hard but if you can do it go for it!
3. making them air dodge into the ground. short hopping right before the enemy is about to land from being up in the air can make them air dodge into the ground giving them all that landing lag, allowing for you to fast fall and do an up smash.
4. Honorary mention of u-air kills at like 150 if they're already in the air when you hit with it, if your really having trouble with a stock
Heres some other random useful stuff that wasn't mentioned
down tilt makes them fall over at certain %'s
down tilt also knocks them at a very unfavourable angle off stage, if their near an edge
You can down smash rolls
getting the thunder spike, but not hitting with the blue part on pikachu makes people panic air dodge a lot.
Left taunt is best taunt
party pika is best hat, also serves as a wizard hat
side b is very good horizontal recovery, but very predictable
you can be dashing one way, then side b the other. For rolls (at low % side b is punish on hit)
up b into the ground has less recovery time than landing after an up b
up b also has more hit stun than previous games, allowing follow ups sometimes
up b is very hard to get the exact angles you want and requires practice
b-air cant be di'ed out of, they can choose if they get hit left or right though (so its not good for edge guarding)
rolling back after starting to run up to them is a way of aborting the commitment
full jump neutral b makes you very safe if they aren't close
