Attribute to set infinite health.

[mibby]

Would it be possible to bring back an option to set mobs as invincible but keep their AI and allow them to be hit? This was possible with the old NBTEditor but no longer with the new one. Was useful for creating invulnerable sheep for ice hockey (no damage but allows them to be swung at / knocked back).

The invulnerable attribute prevents knockback. Before it was possible to specify unlimited health or negative values.