First of all, Murkrow deserves a nomination. As said by those before me, Murkrow is the most dangerous Pokemon in today's Metagame, not only being able to setup on both, Physical and Special threats, but also having said setups with uncontested priority in Mischievous Heart. The fact that makes Murkrow such a dangerous threat to face it's it's umpredictabiliy, much like Salamence in OU back in the day. Murkrow's sets, going from FeatherDance + Calm Mind to Substitute already have few counters by themselves, but when you add the fact that you cannot foresee which set it is, it becomes a very dangerous threat in it's own right. Murkrow's versatility and umpredictability, along various perks like MH Priority setup and MH Priority Roost make it a very dangerous threat which threatens to overcentralize the metagame.
Droughtin itself is also a very dangerous ability, which gives makes Sun Teams extremely threatening in today's metagame. As mentioned by others before, Pokemon such as Bellsprout and Churine take advantage of the everlasting Sun with Chlorophyll, using their movepools which conveniently have all necesarry moves to setup and sweep the opposition. With the inclusion of Evolution Stone, Bellsprout becomes even more dangerous boasting Swords Dance or Growth boosted STAB attacks, Sun Boosted Weather Ball and Sleep Powder as well as Sucker Punch as tools to take advantage of the Sun with. Churine is an often overlooked Pokemon who takes the Sun with a different approach, becoming a very bulky and fast sweeper with access to both, Sun boosted Synthesis and Sleep Powder, as well as the extremely dangerous Growth in addition to powerful STAB Solarbeams from a very good base Sp. Attack. In addition to this, Fire Type Pokemon, already dangerous in their own right, become even better with the power granted by everlasting Sun, with Pokemon such as Houndour taking hte spotlight as the worst threats. The everlasting Sun removes the only weakness fo Sun Teams, which were the turns that their Sun stopped shining, and throws it out of the window, allowing Sun Teams to invest more into offensesand forego Sun setups with Drought in tow. All in all, Drought in itself is a very dangerous ability which may also overcentralize the game to Sun Teams, greatly reducing the variety of viable Pokemon in today's metagame to those that can survive against the onslaught of Sun sweepers.
EDIT: My apologies for the bolds, they have been corrected.
Droughtin itself is also a very dangerous ability, which gives makes Sun Teams extremely threatening in today's metagame. As mentioned by others before, Pokemon such as Bellsprout and Churine take advantage of the everlasting Sun with Chlorophyll, using their movepools which conveniently have all necesarry moves to setup and sweep the opposition. With the inclusion of Evolution Stone, Bellsprout becomes even more dangerous boasting Swords Dance or Growth boosted STAB attacks, Sun Boosted Weather Ball and Sleep Powder as well as Sucker Punch as tools to take advantage of the Sun with. Churine is an often overlooked Pokemon who takes the Sun with a different approach, becoming a very bulky and fast sweeper with access to both, Sun boosted Synthesis and Sleep Powder, as well as the extremely dangerous Growth in addition to powerful STAB Solarbeams from a very good base Sp. Attack. In addition to this, Fire Type Pokemon, already dangerous in their own right, become even better with the power granted by everlasting Sun, with Pokemon such as Houndour taking hte spotlight as the worst threats. The everlasting Sun removes the only weakness fo Sun Teams, which were the turns that their Sun stopped shining, and throws it out of the window, allowing Sun Teams to invest more into offensesand forego Sun setups with Drought in tow. All in all, Drought in itself is a very dangerous ability which may also overcentralize the game to Sun Teams, greatly reducing the variety of viable Pokemon in today's metagame to those that can survive against the onslaught of Sun sweepers.
EDIT: My apologies for the bolds, they have been corrected.