Butterfree will not get you very far past Shelly, so I'd recommend dropping it (and don't pay attention to my trainer card, it's very outdated. Ahahaha.) If you're still looking for a bug type to fit the slot, Yanmega is a much better Bug-Flying, and Escavalier is pretty tough at the cost of being ridiculously slow. I've also heard some good things about Venomoth, so you might want to give that a shot.
X-Scissors on Leafeon is good if you can get your hands on it somehow, I'm not sure there's a TM for it and you can't breed it onto them without travelling BACK INTO THE PAST!! (e.g. Episode 8 or something because mechanics)
If you're looking for something you've never used before, Vanilluxe, Gogoat, & Samurott have all been very useful to me. Drapion is useful too, so I hear, but in my personal experience I've never found them worth training. Maybe I was doing something wrong. Give them a try sometime, if you'd like ^-^ Best of luck!!