Well, Seismitoad is one option. It has a decent attacks and decent bulk, and can fire off both special and physical attacks which is one selling point. It doesn't have the best speed though, so it will take a lot of damage.
Of course, there is the common Basculin, with a good speed and decent offenses. But it is better off with being your Pokemon for Waterfall because of its superior attack stat.
But I like Swanna, who has decent speed and even attacking stats at a fairly decent 87, allowing it to go mixed too. It also serves as a Flyer, another crucial HM (Although Archen can learn it).
You could always just do Jellicent or Alomamola, but they're more defensively based and Alomamola doesn't have very good offensive stats. Stoutland is an option to, but you're better of teaching it to something that has better special attack.
Hope I helped! :)