I imagine that Coco would be a bit difficult to find a good opponent for. If his opponents have tremendous poison resistance, either Coco can't use his main abilities or has to focus on finding a poison that works (which makes for boring fights, imo). If they don't, he can probably easily win.
An intelligent, level headed opponent with speed superior to Coco's and some ranged attacks would be a interesting, challenging match up for Coco. Teppei, Maybe?