As someone who unfortunately gets them far too often, the simplest trick is to give bad care to an odd gen tama. Don't play games often, ignore calls for food/happiness, use snacks to fill hunger, allow it to become ill from bad care (but don't let it be sick for long periods as it risks killing it), leave poops on the screen for awhile, and stuff like that. Training calls can be answered occasionally as I've had many Maskitchis with full training bars, but it's not necessary. Keep in mind though, if you were overzealous with your neglect, your tama is more apt to die because you missed so many care calls to get Maskitchi in the first place. So once you get Maskitchi, take good care of it because at that point, your tama could be one illness from an early grave. Also, note that even if you get good toddlers and teen characters, that doesn't mean you can't still get Maskitchi, Just keep being neglectful and maybe your persistence will pay off.
By the way, it's because I overslept or couldn't care for it properly at school/work which leads to Maskitchi for me. So that might help you a bit with planning but it's easy to get careless with this technique since you might not know how neglectful you've been.
