I noticed this question was never answered; it bothers me when mine get ignored, so I'll help you out. In the stratagy guide, actually, it has listed every person's special value for staying/leaving, and I'm pretty sure you can find it on Serebii too. You pretty much have to beat them and talk to them every day, and eventually they'll migrate over.Right!
Question about Black City and White Forest.
Specifically, entralink! Been googling for god knows how long, now, but no proper answers as of yet.
I've caught all the pokemon in my White Forest, and I want to nab some trainers from my brother's Black City. My brother, too, wants to snag some cats from my White Forest - and he's welcome to 'em, I'm sick of Hoppip and Wurmple and he'd enjoy training against a level 65 Blissey more than I'd benefit from catching yet another Happiny.
However! When I go into his Black City, nobody's interested in coming back in time with me - regardless of how lovely and wonderful they say it probably is. And as much as they covet his Black City, none of my residents abandon my White Forest for it.
Why is this? What conditions do I need to satisfy to make 'em defect? There must, surely, be some hidden value or statistic that I've got to satisfy.
I forgot the numbers, but I think in order to have any chance, you have to visit AND talk to a particular person every day over the course of a few days for them to defect; and some are much harder than others. When you visit, the points towards them leaving go up by 5, but the points toward them staying go down 10 each day, or something like that. So keep at it.