The thing with Lucas is that Peach's F Tilt can outrange and stop his aerials. That's what I've found when fighting him. I need to fight a good Lucas main though to put it into practice
Back onto Ness and Pk Thunder...
I've done some testing and this is what I've found. If Toad connects with the head of Ness' Pk Thunder, it will completely cancel it out no matter where it hits Peach. Peach MUST use Toad at the correct time however, like with all attacks Toad can counter. If the tail connects, Toad will be activated and Pk Thunder will carry on going. However, if spores connect with the Pk Thunder head, it will be cancelled out
It is possible to graze Peach with the tail to set the counter off and then hit her with the head provided the spores don't hit the head
I'd need to fight a good Ness again but regarding Thunder juggling, I'm not sure if Ness would have enough time to mess around setting up the whole tail whip ---> head shot if Peach used Toad
Advice to Peach mains: Watch how Ness uses his Pk Thunder. If you're desperate, I would reccomend Toad. If Pk Thunder is cancelled out, Ness finishes his Pk Thunder animation sooner than Peach finishes her Toad animation but only slightly. Thunder juggling wise, you'll have more than enough time to react to Ness doing something else
Advice to Ness mains: Watch Peach's reactions. The timing for Toad is actually really strict. Peach still has a decent area for error but it's still strict imo compared to other moves. Watch out for her aerials that can cancel out the Pk Thunder head. Aim to tail whip her but be aware of Toad cancelling out the head of Pk Thunder. Tail whipping to set the counter off and then hitting her with the head works but takes extra time
Now I don't main Ness but I was wondering - how will he actually tail whip Peach? (No smart arse remarks like 'use the control stick dummy'). Pk Thunder isn't highly manuverable and because Peach's Nair covers almost her whole body except for the top/bottom, I can't see Ness getting many tail whips without the head hitting Peach's Nair for example. Has anyone got any Peach vs Ness videos where Ness does a good job of juggling Peach, mainly via tail whipping? That would help imo