You can only Special Summon "Black Dragon Collapserpent" once per turn this way
In Standard, even non-typal decks play Cavern of Souls often naming Phyrexian just to make their Atraxa, Grand Unifier uncounterable
9 Animar, Soul of Elements An incredibly powerful commander in its own right, the only reason Animar, Soul of Elements, isn't higher on this list is due to the numerous colors in Animar's casting cost meaning that not all hypothetical hydra decks will be able to run Animar
You can't rely on her flipping without giving your foes the chance to stop her
For example, infinitely flicker Will the Wise with Grinding Station out, and you can stack the triggers to mill the entire table out in a single turn

Abandon Attachments Abomination of Gudul Academy Raider Academy Wall Ajani's Last Stand Akki Ronin Amber Gristle O'Maul Armix, Filigree Thrasher Arrogant Wurm Artillery Enthusiast Artist's Talent Ashling, Rekindled Astonishing Spider-Man Astral Drift Azra Oddsmaker Banon, the Returners' Leader Baral, Chief of Compliance Baron Strucker, HYDRA Overlord Basking Rootwalla Battlefield Scavenger Big Game Hunter Big Wheel Binding Negotiation Bitter Reunion Bloodcrazed Socialite Blurry Beeble Book Devourer Boundary Lands Ranger Brain Gorgers Burning-Tree Vandal Byway Barterer Call to the Netherworld Champion of Wits Chandra's Defeat Chandra's Regulator Chandra, Spark Hunter Circular Logic Cloudpiercer Common Iguana Conspiracy Theorist Containment Construct Contract Hero Cool but Rude Crypt Lurker Customs Depot Daring Saboteur Dark Withering Decree of Justice Demonic Collusion Dictation Quillograph Discerning Peddler Disciple of Deceit Drake Haven Duelist of the Mind Duplicity Ecstatic Electromancer Elaborate Firecannon Erebos's Titan Fable of the Mirror-Breaker Faith of the Devoted Fiery Temper Fissure Wizard Flaring Cinder Flowstone Flood Forbid Force Away Forgotten Creation Formidable Speaker Founding of Omashu Frantic Purification Frenzied Geistblaster
