Theorymon Suicune's a really good mon just in general. OHKO moves are a great way to beat stall and suicune is probably the most viable/consistent ohko move user.
broski wheres the link to amazing mega heracross video resources >_>NOVED takes this week with his Mega Heracross nomination! Having the second highest attack stat in the entire game (not counting abilities) sure does give this thing insane wallbreaking powers.
Speaking of wallbreaking, another hard hitter is Mawile. It gets great abilities, a great typing, and also gets Swords Dance to hit even harder. One of its major downside is its really slow speed, which many teams make up for with one of the best speed control pokemon in the game: Porygon2! Porygon2 has insane bulk that can even survive a Mega Lucario's Close Combat. It has access to Thunder Wave and Trick Room as speed control options to help Mawile clean up the game. What do you nominate to break down this core?