Currently, Modern is about the most powerful it has ever been
* Gargantuans Strategy Card Version 1: White/Green mana symbol instead of Red/Green mana symbol, text is correct
His spoiler is in this card preview article on the Wizards of the Coast homepage

Brago, King Eternal Ultimate Masters Guilds of Ravnica Niv Mizzet, Parun, Emmara, Soul of the Accord, Lazav, the Multifarious (decklist in the comments), Tajic, Legions Edge, Etrata, the Silencer, Izoni, Thousand-Eyed Commander 2018 Aminatou, the Fateshifter, Xantcha, Sleeper Agent, Lord Windgrace, Brudiclad, Telchor Engineer Core Set 2019 Sai, Master Thopterist, Goreclaw, Terror of Qal Sisma, Vaevictis Asmadi, the Dire, Chromium, the Mutable Battlebond Dominaria Teshar, Ancestors Apostle, Grand Warlord Radha, Arvad the Cursed, Muldrotha, the Grave Tide, Slimefoot, the Stowaway, Yargle, Glutton of Urborg, Squee, the Immortal, Firesong and Sunspeaker, Jodah, Archmage Eternal, Tiana, Ships Caretaker Masters 25 Rivals of Ixalan Azor, the Lawbringer, Etali, Primal Storm, Nezahal, Primal Tide, Zacama, Primal Calamity, Tetzimoc, Primal Death, Zetalpa, Primal Dawn, Ghalta, Primal Hunger Unstable Grusilda, Monster Masher, Dr

You can currently get a mythic rare borderless Vivi Ornitier card for less than $300, though there are some better (and cheaper) legendary creatures to build a commander deck around