I would imagine a SleepTalker would be very annoying to deal with, because of the always present chance to paralyze with Static while tanking. Swampert´s defenses were a disappointment for me, but as it was very popular, I might as well could give this guy a chance too.
Maggyo@Leftovers
252HP 252Def
+Def -Atk // Static
- Thunderbolt/Discharge
- Earth Power/Boiling Water
- Sleep Talk
- Rest
The reason I went fully physical defensive on the EVs is that most ice, grass and water attacks are special, so he can´t really use a special split, imo. The idea is to switch this into neutral/ineffective contact moves and hope for Static to kick in(for team support). When the need arises, rest up and let the fun start again. In theory, your opponent should be much more cautious of using contact moves carelessly, as it could very well cripple a sweeper of his team.
Only letdown here are the new sleep mechanics, which make resting up a second time kinda hard.
On being grass type lure, I must say that this isn´t necessarily a bad thing. Most used Grass type right now, outside of DW mode, is Nattorei, which is setup bait other bulky sweepers, such as Zuruzukin and Roobushin. That said, I´d totally use Maggyo to open up boosting possibilities for these threats.