I think Breloom can viably run a set with Mach Punch *and* Power-Up Punch without wasting a move slot. Add in Rock Tomb to get back Low Sweep's coveted speed drop and either Bullet Seed or Seed Bomb (depending on your preference) for another STAB.
I only recently tried this, so I'm not sure how it'll work out, but I suspect it'll be just as good. It gets a smaller attack boost in Power-Up Punch, but it hits back, unlike Swords Dance. Rock Tomb also counts for good coverage with it's Technician boost and the aforementioned secondary effect. Mach Punch compensates for Breloom's mediocre speed. Add in the other grass STAB of your choice (I think both are pretty alright) and it still has a boosting move, two STABS, good offensive coverage and it still lowers speed. *And* has priority.
I think my biggest problem is that Power-Up Punch relies on actually hitting for you to get a boost. Even though it has great accuracy, for multiple reasons, it could be rendered useless. Whereas Swords Dance will work through pretty much anything; it's much harder to effectively stop.
I only recently tried this, so I'm not sure how it'll work out, but I suspect it'll be just as good. It gets a smaller attack boost in Power-Up Punch, but it hits back, unlike Swords Dance. Rock Tomb also counts for good coverage with it's Technician boost and the aforementioned secondary effect. Mach Punch compensates for Breloom's mediocre speed. Add in the other grass STAB of your choice (I think both are pretty alright) and it still has a boosting move, two STABS, good offensive coverage and it still lowers speed. *And* has priority.
I think my biggest problem is that Power-Up Punch relies on actually hitting for you to get a boost. Even though it has great accuracy, for multiple reasons, it could be rendered useless. Whereas Swords Dance will work through pretty much anything; it's much harder to effectively stop.