Breloom is a mediocre pokemon in Ubers - too slow, fragile, and its Mach Punch lacks the power to break most Uber Pokemon not named Darkrai, Terrakion, Dialga, Kyurem-B/W, Ferrothorn, Excadrill, Kabutops, and Arceus-Ste/Rock/Dark (okay quite a list here, but handful of these KOs wont be attained without attack boosts). Granted Sleep Clause may give Breloom *SOME* justification to use - but just like how stacking up on OHKO moves haven't seen much effectiveness (as explained by syrim and Poppy), stacking up on Sleep Inducers doesn't seem like a sound strategy, either. The major abuser of Sleep Clause is Darkrai. I guess, syrim is right that there will be lots of 50/50s, but I find them more strategic than say clicking an OHKO move and pray for a lucky break. Still, even OHKO clause warrants a proper test to truly evaluate whether its risks balances out the enormous reward.