As you know, after defeating Gigas, Ness and his friends' spirits left their robot bodies in the past in order to return to their real bodies in the present. What you don't know is they made a small mistake along the way. A small but terrible mistake.
Poo was in a hurry to return to his own body, in his haste he bumped into Jeff, it sent them both flying. That in itself was a catastrophe but not near as catastrophic as the event it caused, Poo's spirit landed in Jeff's body and Jeff's spirit landed in Paula's body.
While this was occurring, Paula's spirit leaned in close to Ness's body. Staring at him. He's so cute when he sleeps! She couldn't help but think. She leaned in closer, and closer, then by accident she leaned in a bit too close. Close enough now for her spirit lips to touch his physical ones, and for an instant they did as she stole a quick kiss, in a split second her spirit was in his body.
Ness alone now lacked a body; his was taken so he went to the only available one, Poo's.
This could get interesting.
"Yes you all made it back safely, the world is saved!" Dr. Andonuts exclaimed as soon as he realized that the four children had begun to stir, not realizing the terrible event that had occured
"I thought you were supposed to be the smart one! Why didn't you get out of my way!" Poo yelled from within Jeff's body
"well SORRY, do you think I would do this on purpose! Maybe if you weren't going so fast in the first place!" Jeff/paula replied
"since when was Paula the smart one? I would have that would be you Jeff" Dr. Andonuts said with a slightly confused expression on his face
"I am Jeff"
"But you're a … girl" Dr. Andonuts pointed out
Jeff looked down then said "for the moment that may be true, but I assure that I most certainly am your son, Jeff"
"I will clear this up, due to unforeseen circumstances" Ness/poo said "I'm Ness in Poo's body, Poo is in Jeff's, Jeff is in Paula's, and Paula is in mine"
"so what now" Paula/ness asked looking at Ness/poo
"why do you instantly assume I know what to do?"
"because we've made it this far on your decisions why stop now?" Jeff replied
"ok fine" Ness said "Let's go get some drugged… I mean Magic Cake!"