We are at a point in our Surging Sparks format where there is a clearcut best deck in format, and that deck happens to be Regidrago VSTAR [Silver Tempest]
Four mana seems steep, but the added protection is well worth it when youre gearing up to close out the game
Legendary builds are so diverse from Shrines to planeswalkers to legendary pals and historic matters
Entropic Uprising supports this heavily by running tons of Wheels (Runehorn Hellkite, Dragon Mage, Wheel of Fate, Windfall, Ancient Excavation, Whispering Madness) and then a bunch of ways to take advantage of all those discarded cards / filled graveyards with stuff that reward you for your opponents discarding (Nath of the Gilt-Leaf, Sangromancer, Waste Not) or for having filled graveyards (Guiltfeeder, Spellheart Chimera, Worm Harvest, Ghastly Conscription)
The cost reduction Jhoira's Familiar provides is good with legends, artifacts, sagas, and makes several loop combos viable like Mystic Forge + Sensei's Divining Top
I think youre getting pretty solid value here, between getting some ramp and venturing into a dungeon