So, you've taken an existing map, then added a simple edit of Animate Dead, a simple edit of a Ghost unit and this trigger:
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Zombification
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Events
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Conditions
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((Triggering unit) is A structure) Equal to False
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((Triggering unit) is Mechanical) Equal to False
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((Triggering unit) is Summoned) Equal to False
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((Triggering unit) is A Hero) Equal to False
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((Triggering unit) is Undead) Equal to False
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Actions
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Unit - Move Ancient Lich 0149 <gen> instantly to (Position of (Dying unit))
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Wait 2.00 seconds
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Unit - Order Ancient Lich 0149 <gen> to Undead Death Knight - Animate Dead
I'm sorry, but that's really not a lot of effort.
The mechanic itself is simple, but it works and is decently fun. If you made your own map instead of using an existing one (sorry, but that's just lazy), perhaps using like a slightly modified Felwood tileset with a selection of spooky doodads, creep and fog effect to get more of a hunted forest vibe, then added a couple more mechanics that match this theme, for instance some ghosts roaming the forest and casting curses or hexing encountered units, or some trees spawning corrupted treants when they die... Then throw in a handful of custom items that also fit that theme and you could get a really fun and interesting altered-melee halloween map.
Sadly, what you did isn't it - it's just a regular melee map with a fun, but very simple and not very impactful mechanic that took minimum effort to implement. I'm sorry, but for me that's not enough.