General configuration applies to every Undead mob, unless explicitely specified.
Undead: Phantom, Skeleton, Stray, Wither Skeleton, Skeleton Horse, Zombie Horse, Zombie, Zombie Villager, Drowned, Husk, Zombified Piglin, Zoglin, Wither.

❤️‍🩹​ Steal Health

Undead steal health of their target on attack.

Description

• Every Undead mob, except The Wither, heal as much as they damage.
  This doesn't apply to the Wither, that already has such a feature in vanilla.
• They can't heal more than their maximum health.

💑​​ Undead Friendly Fire

Undead ignore other Undead attacks.

Description

Every Undead mob don't take revenge on other Undead mobs.
This is useful only for Skeletons, or other Undead ranged mobs.

Configuration

The General configuration can be found in .minecraft/config/sihywtcamd/undead.json.

• attackHeal: [true|false] to enable/disable undead stealing health
• ignoreUndeadAttacks: [true|false] to enable/disable undead ignoring undead attacks