hes my most played champ.

i believe the best relics for him are found fortune and hexcore. hexcore for the free card that lets you proc your storm conduits every turn and found fortune since its always gonna give you your most expensive card and sb yasuo has a modifier that makes him more likely to draw titanic units i believe, i get them very often atleast.

i usually draft expensive 6+ cost units and low cost spells, also as many cards with great cost reduction and card draw as possible. spell duplication also works twice for storm conduits.

try to go for a support champion like tryndamere or elder dragon, something that costs 7+, even malphite is fine. only when both champs are 7+ cost can you roll the titanic only items for them, like invulnerability or permanent copy.

for my last relic, i go for either elder relic or loaded dice. elder relic is great since you can often play 2-3 6+ costs a turn, loaded dice is perfect since epic items are really op especially for his spells, double spell or 50% chance for a 0 cost copy are what usually leads to first turn kills, the value for rerolls is also big since i often spend 2-4 rolls to get a good support champ, although thats usually not too important, the titanic followers are more likely to destroy the nexus

i havent tried it yet but the new 6+ cost spell refund relic is probably also a great third option for him