When you summon a custom mob with "{Invulnerable:1}" tag, you can hit the mob. It's not invulnerable.
MC-56204
Invulnerable tag doesn't work
Resolved
Duplicate
0
(Unassigned)
Unconfirmed
Minecraft 14w20b, Minecraft 14w21a, Minecraft 14w21b
Retrieved
you're in creative, that's intended, switch to survival or adventure
duplicate of MC-51195 if you have not please use the search function in the future