Breloom

Breloom is the most reliable sleep inducer, thanks to Spore, the only fully accurate sleep move. It exploits sleep excellently with the most powerful Focus Punch in OU, possibly 2HKOing even physical walls and resistant switch-ins like Skarmory and Zapdos. To generate Spore opportunities, it makes use of its great defensive typing to switch into Water-type attacks from Swampert, Milotic, and Suicune and Crunch from special Tyranitar. It also resists the Rock Slide + Earthquake coverage of the tier's most potent physical threat: Tyranitar. To top it off, Breloom has Mach Punch to revenge kill Dragon Dance Tyranitar, limit Dugtrio's ability to revenge kill it, and generally finish off weakened foes.

Breloom, however, is incredibly frail, and the Pokemon that it switches into frequently carry moves like Ice Beam, Fire Blast, and Focus Punch that can severely damage or OHKO it. Breloom is also rather slow; while it can outspeed most defensive Pokemon, the vast majority of offensive threats can easily revenge kill it. Breloom also has poor coverage; it relies on a weak Hidden Power or status moves to cripple Pokemon that resist Fighting. This limits its utility outside of the initial Spore + Focus Punch sequence, lets Ghost-types and Psychic-types with Recover wall it, and renders it setup fodder for Dragon Dance Salamence and Gyarados. Finally, Breloom is easily trapped and revenge killed by healthy Dugtrio.