I have had a Paparatchi. Here are my tips for getting both them. Please note that I won't guarantee anything.
Paparatchi: I think Paparatchi is a Tarakotchi -care level character, so you need to take average care. I played a game for a happy heart sometimes, and gave a snacks for a happy heart sometimes. Training points were full. Odd generation is a must.
Megatchi: I haven't had a Megatchi, but I think it's a Masktchi & Gozarutchi -care level character, so that means poor care. Your teen should be quite spoiled with snacks, and weighting 99lb helps to get a Masktchi & Gozarutchi level characters. Odd generation. That kind of care could also result a Masktchi or a Kurokotchi, though.