[X] A war of sabotage. Don't give them a chance. They can't catch you if their Pokeballs fail, their gadgets go missing, their clothes char and their supplies get spoiled. Give them hell.
[X] Silk-Choked Streets. With the threat of financial loss and humiliation on the table should they cross paths with you, trainers are sticking more and more to the most well-trod routes through the forest. But this has given silk-spinning Bug-types the opportunity to thrive elsewhere, and many paths through the Forest are now all but impassable.
[X] Proud. If your mischief has pushed them to the point of bringing people in just to target you, you're clearly doing something right. Do more of it.
[X] A wild mouse chase. Make them work for it. Lead them around the Forest by the nose, bedevil and beleaguer them at every step, until they turn around in frustration and give up.
[X] Beedrills and Butterfrees. With so few trainers able to capture the many Weedles and Caterpies of your home, their adult forms are swarming in greater and greater numbers. Soon they will grow beyond the Forest's ability to support them - and respond with a great Migration that will take them through Human lands at potentially devastating cost.
[X] A Plague of Pests. No longer willing to risk the formidable swarms of the deeper forest, wild Pidgeys and Rattata have turned to Viridian City for their food. Crop fields and urban gardens alike are being stripped bare, pantries and larders are being raided, and hungry, feral Pokemon are taking up residence under sidewalks and along rooftops.
[X] A head-on offensive. Let them come. You'll meet them - not with "fair" fights, but with an arsenal of tricks, traps and taunts to send them scurrying away with their heads hung low.