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
UR Ultra Rare Red Blossoms from Underroot X DARK Level 1 [ FiendEffect ] ATK 0 DEF 0 If this card is in your hand: You can target 1 Spell/Trap in each GY
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)
Since Rise of the Floodborn features zero six-drops at common, the desirable ones are at an even higher premium if you would like to fill out your curve
Four mana seems steep, but the added protection is well worth it when youre gearing up to close out the game
I think youre getting pretty solid value here, between getting some ramp and venturing into a dungeon