Sacrifice after III.) I, II Create a Treasure token
It lets you sacrifice a creature to draw cards equal to its power, then discard three, which often nets you a huge chunk of your deck

Agatha of the Vile Cauldron Anax and Cymede Appeal // Authority Appeal // Authority Archetype of Aggression Arlinn, Embraced by the Moon Balmor, Battlemage Captain Baru, Fist of Krosa Become Brutes Bleeding Effect Blossoming Bogbeast Boom Scholar Cabaretti Charm Cactusfolk Sureshot Campsite Cuisine Centaur Chieftain Concerted Effort Conclave Guildmage Crash Through Craterhoof Behemoth Decimator of the Provinces Dinosaur Stampede Domri, City Smasher Dragon Throne of Tarkir Driven // Despair Driven // Despair Drover Grizzly Earthshaker Giant Ellywick Tumblestrum End-Raze Forerunners Engineered Might Ezuri, Renegade Leader Fangren Pathcutter Garruk Wildspeaker Garruk, Wrath of the Wilds Garruk, the Veil-Cursed Glacier Godmaw Glorious Sunrise Goblin Slingshot Graphic Violence Greenbelt Radical Heroic Charge Hideous Taskmaster Horned Sliver Huatli, Warrior Poet Humbler of Mortals Hustle // Bustle Hustle // Bustle Invigorated Rampage Jubilation Kamahl, Fist of Krosa Kamahl, Heart of Krosa Kenrith, the Returned King Kenrith, the Returned King Kneel Before My Legions Kobold Drill Sergeant Legion Loyalist Leonardo, the Balance Lisette, Dean of the Root Lorehold Charm Mishra, Lost to Phyrexia Myojin of Towering Might Najeela, the Blade-Blossom Najeela, the Blade-Blossom Najeela, the Blade-Blossom Nature's Blessing Nissa, Ascended Animist Nissa, Nature's Artisan Odric, Lunarch Marshal Ondu Champion Overcome Overrun

This variant of Hydreigon ex is number 240 in Surging Sparks