"I cannot think of any mod or ability that would prevent these knockdowns"-Inaros' augmented Scarab Armor-Atlas just standing there-Gauss' Kinetic Plating-Nezha's Fire Walker (Subsumable, but only the lingering flames provide immunity = only useful when you stay in one area for some time)-Nezha's Warding Halo-Nidus' Parasitic Link-Rhino's Iron Skin-Frost's augmented 4-Revenant's Mesmer Skin-Oberon's Hallowed Ground-Titania's Spellbind (Subsumable) (yes, it provides knockback/down immunity. Did you make sure to hold the cast?)-Trinity's Link-Yareli's Merulina-Ember's augmented 3-Nekros's augmented 4-Ivara's augmented Quiver thing-Hydroid's Tidal Impunity-Valkyr's Hysteria (if the melee is out, so not very useful)-Nyx's AssimilateAnd for everyone else:-Primed Sure Footed (Exilus)-various other knockdown protection mods with less percentage)