Abilities were awesome addition to the series, so I was wondering how something like skill trees would work.
My idea was to give skill trees to Pokemon dependent on their type. something like abilities for types. For example, poison types could have a skill that make poison type attacks super effective against water types or poison types could have a skill that allows them to hit steel types, but instead of doing damage it would lower defenses (not these skills exactly, but I hope you get the idea).
The idea is not fully fleshed out yet, but does it sound good?