Invulnerability is an effect that reduces all damage taken to 0 (except pure damage) and is the only form of damage reduction that affects true damage. Drain effects, such as life steal, will have no effect against invulnerability. An invulnerable champion wearing 
Thornmail will still reflect damage, as Thornmail's damage reflect occurs before damage reduction.
Fiora's 
Riposte (excluding turret damage)
Kayle's Intervention- Kindred's Lamb's Respite
- Kog'Maw's Icathian Surprise
- Taric's Cosmic Radiance
- Xin Zhao's Crescent Guard (excluding enemy units within Awareness area)
- Golden Transcendence
Stasis effects:
- Aatrox's Blood Well
- Bard's Tempered Fate
- Kalista's Fate's Call
- Lissandra's Frozen Tomb
- Shaco's Hallucinate
- Zilean's Chronoshift
- Guardian Angel
- Wooglet's Witchcap
- Zhonya's Hourglass
Invulnerability may occasionally be used to refer to:
- Undying Rage, although this only prevents Tryndamere's health from being taken below a certain amount and it does not actually reduce the damage inflicted.
- Untargetable effects, such as Vladimir's Sanguine Pool or Fizz's Playful / Trickster. However, these effects only prevent you from being targeted or affected by area of effect
- Being untargetable does not prevent you from taking damage, such as from an active damage over time.
