Platinum Angel: The core of this hard lock. It guarantees that no alternate win condition or mill will break this combo.
Mycosynth Lattice, Darksteel Forge, Hanna's Custody (a suggestion from Bovine073), Stony Silence: All permanents now have shroud and indestructible and can't activate any abilities, even mana abilities.
Orbs of Warding, Sigarda, Host of Herons: I have hexproof and can't be forced to sacrifice any permanents.
Angel of Jubilation: This card prevents creature sacrifices and life payments to cast spells, preventing effects like Ichor Explosion and Toxic Deluge.
Gaddock Teeg: Every mass exile and mass bounce spell that affects permanents, with two exceptions, costs at least 4 mana. The two exceptions are Martyr's Cry and Cyclonic RiftGC. This card prevents almost every other mass bounce and mass exile effect.
Knowledge Pool, Rule of Law, Teferi, Mage of Zhalfir, Erayo's Essence
: This creates a near hard lock: You can cast only one spell per turn, and it's automatically exiled if you cast it from your hand, or countered if you didn't. Teferi prevents casting off Knowledge Pool, which would break the sorcery-speed only restriction.
Melira, Sylvok Outcast: This card prevents the spreading of -1/-1 counters, such as Carnifex Demon and Black Sun's Zenith, to remove my creatures.
Torpor Orb: This card prevents "enters the battlefield" triggers. Perhaps you have a Standardize and Karrthus, Tyrant of Jund suspended with Jhoira of the Ghitu
about to enter the battlefield. You don't get anything from me.
Xenograft: This card is added in response to chaosumbreon87's method of flipping Thing in the Ice
to bounce all non-Horror creatures. Now my creatures are Horrors, too!
Stabilizer: This prevents cycling effects like Decree of Pain, Decree of Justice, or Archfiend of Ifnir.
Rest in Peace: Offered by Zaueski to stop a potential Living End line.
Eon Hub: This prevents forced phasing from Teferi's Realm and any suspend effect that might sneak in. This was a suggestion from zephramtripp, filling a hole created by Sunken Hope and Teferi's Realm, while also blocking any suspended cards that might somehow sneak through.
Iona, Shield of Emeria, Painter's Servant, Light of Day: this prevents casting any spells that could be copied by Mirari or Djinn Illuminatus. As long as Painter's Servant is set to to , it also prevents Lure + Sword of Kaldra
from exiling my creatures, as well as the artifact theft ability of Hellkite Tyrant. Additionally, as aholder7 pointed out, Avatar of Slaughter equipped with Godsend would be able to force my creatures to attack and be exiled.