The Ancient unit tag causes the tagged units to be treated differently by spells and other effects. It also turns them completely immune (i.e. untargetable) for some spells, mainly spells which instantly kill the target.
The following units are ancient creeps: Ancient Black Dragon, Ancient Black Drake, Ancient Granite Golem, Ancient Rock Golem, Ancient Thunderhide, Ancient Rumblehide, Ancient Prowler Shaman, Ancient Prowler Acolyte, Roshan, Animal Courier, Flying Courier, Earth, Storm, Fire, Void, 
Astral Spirit, Familiar, Warlock Golem, 
Tombstone.
Spell interactions[]
If a spell has different effects on heroes as it does on creeps, then it uses the creep effect on ancient creeps. For example, spells with different durations on creeps than on heroes use the creep duration.
Not affecting[]
The following spells are unable to target or affect units tagged as ancients.
Bane – Enfeeble- Chen – Holy Persuasion1
- Clockwerk – Power Cogs
- Dark Seer – Vacuum
- Doom – Devour2
- Doom – Doom
- Elder Titan – Natural Order
- Elder Titan – Earth Splitter
- Enchantress – Enchant3
- Enchantress – Nature's Attendants
- Enigma – Demonic Conversion
- Enigma – Midnight Pulse
- Hand of Midas – Transmute
- Helm of the Dominator – Dominate
- Keeper of the Light – Blinding Light
- Nature's Prophet – Sprout
- Necrophos – Heartstopper Aura
- Outworld Destroyer – Arcane Orb
- Pangolier – Rolling Thunder
- Pudge – Meat Hook
- Shadow Demon – Soul Catcher
- Spirit Bear – Entangling Claws
- Vengeful Spirit – Nether Swap
1 Can target ancients when having Aghanim's Scepter. Still cannot be cast on creep-heroes.
2 Can target ancients after the required 
talent is chosen. Still cannot be cast on creep-heroes.
3 Can target ancients after the required talent is chosen. Still treats creep-heroes as heroes.
Unique[]
The following spells treat units tagged as ancients differently than regular creeps.
- Uses the hero duration against ancient creeps, rather than the creep duration.
- Does not root enemy ancient creeps like how it does when used on regular creeps.
- Cannot be cast on ancient creeps to smash them. Ancient creeps are affected by the damage/slow normally.
- Cannot be cast on ancient creeps. Can jump onto ancient creeps and damage them normally.
- Cannot be cast on ancient creeps when on level 1. Can target them normally when on level 2 or 3.
- Does not instantly kill ancient creeps like how it does when hitting regular creeps.
- Does not affect/damage enemy ancient creeps. Does affect/heal allied ancient creeps.
- Does not affect ancient creeps when passing through them. Does affect ancients while stationary.
- Does not affect ancient creeps when passing through them. Does affect ancients while stationary.
- Cannot toss ancient creeps. Can target ancient creeps to toss units towards them.
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