Mobs will not use shields, and the shields themselves are purely visual; they don't block projectiles such as arrows.
Effects on different mobs that have visible held items:
Skeletons and Strays: Use their melee attack (the one they use when holding something other than a bow)
Pillagers and Illusioners: Don't attack (
All other mobs: No difference in behavior
How to reproduce (easily):
- Summon a mob without any held item that has "CanPickUpLoot" set. Example:
2. Throw a shield at the mob, wait for it to pick it up, and shoot an arrow at the mob's shield
→ Notice the arrow going through the shield and hitting the mob, dealing damage to it.