I guess I'll give my thoughts on Pichu because I'm bored.
I'd be somewhat okay with Pichu coming back but obviously he needs to be reworked fairly substantially. Due to his super low weight, I don't think he can be anything other than a glass cannon, he's fast and hits hard but can't take a hit to save his life. Also, obviously the self-damage mechanic remains but it needs to be reworked to make him not useless.
The way I see the self-damage working is like Solarbeam but in reverse. As Pichu hurts himself, he also builds up a powerful one-time use special attack. As a million other people have suggested, this should probably be Discharge, since he's releasing the static electricity he's built up. The way I'd see this working is that it creates a radial shockwave around Pichu. If he has not hurt himself, it does minimal damage, has virtually no range, and little knockback. However, if you have hurt yourself for say, 30%, it creates a massive burst around Pichu that has high knockback, probably KOing around 80% (of course, with lesser damage it's somewhere between those two extremes). Unlike Ivysaur, if Pichu dies, you lose the charge, so there's a risk / reward to charging it up too much.
I would probably map this attack to Neutral B. This means that something has to happen to his existing moves, probably the elimination of Skull Bash and the moving of his projectile to Forward B. I also might change up his projectile a little, though I'm not exactly sure how.
I would also adjust Agility. It would still not do any damage, but it no longer leaves Pichu helpless, complimenting his status as a hyper-offensive character. Of course, you can only use it once per jump, and no Agility Cancel for Pichu.
As for Thunder, I might consider giving it its Smash 4 property (which was just revealed today), if the bolt hits an opponent they get meteor smashed. This seems to have crazy combo applications, which is perfect for Pichu. I also might consider removing Thunder 2 altogether, so it doesn't prevent you from doing a follow up if the beam hits (but Pichu still gets damage from taking a thunderbolt to the head).