I need Trigger for Holy Light ability to Auto Cast

[Captain Luc Valonforth]

I need Holy Light Skill to auto cast with a new Trigger. When my Paladin close-up to Allied Unit with the little life, They will Auto cast the Holy Light. Same happen when Undead try to attack my Paladin. They will Auto cast Holy Light to Undead.

 

[Bender]

You'd need to find an autocast ability that inherently targets both non-undead allies and undead enemies, and trigger Holy Light accordingly, which is... Unlikely, to say it kindly.

 

[Duckfarter]

Triggers could be something like:

unit is attacked / takes damage
attacked unit = paladin, attacking unit = enemy, attacking unit = undead, attacking unit not mechanical, not structure, current order = empty string, mana greater than 65, distance less than 650, life of attacking unit greater than x
Issue order Holy light

every 1 seconds of game time
pick all paladins
dead = false, current order = empty string, mana greater than 65
pick units within 450
picked unit dead = false, picked unit = friend, picked unit not undead, picked unit not mechanical, picked unit not a building, max life - current life greater than x
Issue order Holy light

 

[Warseeker]

I need Holy Light Skill to auto cast with a new Trigger. When my Paladin close-up to Allied Unit with the little life, They will Auto cast the Holy Light. Same happen when Undead try to attack my Paladin. They will Auto cast Holy Light to Undead.

For healing allied units, you could base your ability on the Priest's Heal ability and change its effect to look like Holy Light.
As for damaging undead units, if you can make the Priest's Heal ability work on enemy units as well, then you could detect when this ability is casted on an enemy undead unit and reverse the damage. If not, then you could give your Paladin a hidden autocast ability that targets enemy units (e.g: Faerie Fire) and use this ability to damage undead units when casted. You may also want to make your base ability share the same cooldown as the hidden ability.