Minecraft wiki entry for NPC, associated text: An NPC instantly dies when going below Y=0 and makes player death sounds as it vaporizes or if it gets hit in creative mode.
The player can summon an NPC in Bedrock Edition by either using the command /summon npc or /give @s spawn_egg 1 51.
Zoglins, withers and vindicators named Johnny attempt to attack NPCs. The NPC remains undamaged, as NPCs are invincible. However, the mobs still continue to attack.