It seems to me that a lot of the designs around here aren't really taking the stats that people are throwing around into account, so here's mine. Looking at the stat thread, X-Act's stats really fit.
I took the spider concept and played with it. Six of the eight legs make up the two hands, which works with a utility pokemon's flavor, at least for me. It's smaller, and skinner, so the speed everyone keeps talking about fits and looks right. We don't want a Snorlax-like pokemon outrunning Garchomp.
The spider's abdomen-ass thing is placed on its back, to be used as armor or a shield, providing the higher defenses people are looking for. I can also see her lying on her stomach, arms tucked in, running around on her fingertips like a normal spider, with her massive back completely protecting her.
The color scheme is very important. Pokemon look out of place if their colors don't match the color scheme designated for each type. Poison has been given purple, so her shield is purple. Ground pokemon stick to earth tones, mostly brown, but a variety does exist. Since poison is the dominant type, i went with the most "poisonous" of the earth tones, green, and went straight to acid green. The black widow sign is hidden in the center of her chest to emphasise (and make sure it's understood that she's a spider-creature). It'd be on her back as well, if I drew the other side.
The only thing I'm really uncertain about her is her shield-abdomen-back thing. Depending on how big the defences get, it could double in size to be appropriate, if not more.