Giving all Creatures your opponents control just one toughness leaves them very vulnerable to many Black board wipes, like The Meathook Massacre, Toxic Deluge, Nuclear Fallout, and Black Sun's Zenith
In Modern, it's been enabled both by Ruby Medallion becoming a legal option for Modern, and a new MTG planeswalker card, Ral, Monsoon Mage - which we saw spiking last week
Since then, it has become such a prevalent part of the Modern metagame that there is a whole category of blue and red spell decks built with Murktide Regent in mind

Alela, Artful Provocateur Aminatou, Veil Piercer Arna Kennerd, Skycaptain Bane, Lord of Darkness Chromium Chromium, the Mutable Dakkon Blackblade Dromar, the Banisher Elenda and Azor Eriette, the Beguiler Ertai, the Corrupted G'raha Tia, Scion Reborn Halfdane Inquisitor Greyfax Kamiz, Obscura Oculus Lady Evangela Marneus Calgar Merieke Ri Berit Nevinyrral, Urborg Tyrant Nihiloor Noctis, Heir Apparent Noctis, Prince of Lucis Oloro, Ageless Ascetic Queza, Augur of Agonies Raffine, Scheming Seer Ratonhnhak:ton Saruman of Many Colors Sefris of the Hidden Ways Sen Triplets Sharuum the Hegemon Sidar Jabari of Zhalfir Soundwave, Sonic Spy Sydri, Galvanic Genius Temmet, Naktamun's Will The Destined Warrior The Ever-Changing 'Dane The Master of Keys Tivit, Seller of Secrets Toluz, Clever Conductor Urza, Chief Artificer Varina, Lich Queen Y'shtola, Night's Blessed Yennett, Cryptic Sovereign Zur the Enchanter Zur, Eternal Schemer

Example: If your deck focuses on removing the enemy Pokemon's Energy, you should include several Energy Removal and Super Energy Removal cards
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