I haven't played Pikachu in Smash 4 for a while now. I've been messing around with other characters *cough* R.O.B. *cough*
The list of characters I've been using aside from my "top 5" (Pikachu, Toon Link, Rosalina & Luma, Sonic, Dark Pit) has gotten extensive and at this point several characters have gotten a very promising playstyle for me and are comfortably possible at breaking into my top 5. I've been using Jigglypuff, Donkey Kong, Sheik, Pac-Man, Mewtwo, all to moderate success whereas I've also been using and enjoying Meta Knight, R.O.B., Falco, Captain Falcon and a couple of others and not doing terribly with them either.
Honestly my Jigglypuff, Pac-Man, and Sheik all might be capable of taking out Sonic or Dark Pit in my top 5, but I dunno. I haven't shown too much improvement with Sonic lately but Dark Pit I go back to on occasion and find I'm still decent with him.
R.O.B., is really nice but I've found several key moves I like of his have bad startup lag causing me to get hit before I execute the attack. Reading isn't my best skill in Smash so I kinda need characters with less laggy moves, hence why I've improved a lot more as say, Jigglypuff whose moves don't have a lot of startup.