A steel or ground type might work in your team (checks rock types who would destroy yanmega and arcanine). Steel type especially would be useful because of poison immunity, so I'd say swap Arbok out for like an Aggron or something. For ground types you can try Swampert, who would also add those tasty Water moves to counter fire and ground types that would hurt Meganium, Garbodor, and Yanmega.
Jolteon can outspeed and take out almost anything in 1-2 hits.