This round's unbanned
Pokemon abilities:
Drizzle, and later Drought, were once deemed to be broken. They made scenarios in which weather abusers such as Mega Houndoom and Venusaur, and Kingdra and Kabutops, respectively, had their great boost in stat(s) just by the summon of the respective weather summoner. Not only did Drizzle, especially, grant its abusers a boost in their Speed, but also powered up the power of their STAB move, which was absolutely devastating to deal with. While Drought did not grant its abusers a boost in their STAB move because most of the abusers were not Fire-types (e.g. Venusaur, Victreebel), it did cause the ban of Mega Houndoom, which was undoubtedly really powerful under the sunlight.
However, UU does have the tools to stop these abilities from wreaking havoc in the tier. Common Pokemon like Empoleon and Primarina check Drizzle's best abusers in Kingdra and Kabutops, respectively. While Kabutops does have the potential to break them with Swords Dance + a Z-move, Kabutops has a hard time setting up because of its underwhelming defensive typing. Furthermore, it has to forgo either Aqua Jet, Swords Dance, or Rapid Spin, to run Fighting coverage. As for Mega Houndoom, it can only do massive damage under very certain circumstances. Not only does Sun have to be up, but it also has to set up either a Nasty Plot or a Flame Charge (or both), which isn't achieved easily because of its weakness to Stealth Rock, the fact it loses some of its HP every turn because of Solar Power, and because of its average defensive typing.
Nevertheless, these abusers in conjunction with the setters would undoubtedly be really good in the metagame. Would they be broken, though? We are here to find that out!
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