Just looking for a list of all sp damage reductions whether it's spells, equips, relics, champ abilities.
You really should just look through all of the SP runes yourself... But I'll list some of them. These are some SP runes that either directly or indirectly reduce damage: Earthshaker's Bracelet Idol of Elements Lightning Rod Ol' Sok Headsrhinker's Totem
Voil Infernal and Hyaenid Witchdoctor with Hex and Hyaenid Headshrinker all have great dam reduction. They also come with great utility and are top tier includes.
U also have stuff like Spike Ghern helm (redirects some dmg Pawn) Whispers of the mind Zealotory Boulder Throw In a way u can also add Rock trap, and stuff like stall.
Tempest Crown and Arroyo Echo, if you want to count HP buffs then you cant beat magnify beast. Yay Super is going to play SP! I wonder what you have got planned but it sounds good. My advice is to run Arroyo Echo its got Dread Field + Stall. Dont forget the Cyclops Rockshapers if you can afford them for Boulder Throw and dont forget Boulder Throw and Rip.