The deadliest of the Infested units, Toxic Ancients are constantly surrounded by a poisonous cloud that lingers for a short while even after one is slain. Just being close to them will induce poison damage (which bypasses a player's shields), making melee combat a very poor tactic against these Ancients; interestingly, their arm attacks do not poison players.
Toxic Ancients can be identified by the bright green glow from their heads, as well as their black and green bodies.
The toxic properties may be the result of a kind of decomposition, purposeful or accidental due to the plague. It is also noted that Toxic Ancients may be slightly faster than other Ancients, and will deliberately charge the player until it decides to hit you or run directly into you. They seem to attempt to get closer to you more than the other Ancients.
If a Tenno enters stealth while an Ancient is charging into attack range and remains in the same position, the Ancient's first attack will still connect but it will not continue to attack until its target becomes visible again. This may actually be counterproductive for the Toxic Ancient as the attack will often knock the invisible Tenno out of poison range.
- While under the effect of Nyx Mind Control the Toxic Ancients poison will no longer harm you or your Team, but the cloud they leave on death is still harmful.
- The cloud stays for approximatively 10 seconds after the death of the Toxic Ancient.
- The cloud and the presence of a Toxic Ancient can damage a cryopod on defense missions.
- Prior to Update 9, A Toxic Ancient shrunk if Stealth Attacked.
- In alert assassination missions, the target is sometimes a Toxic Ancient. They still drop blueprints on death as the target of that planet would.
- Ancients will continue pursuing you if they have locked on to you after you have entered their sight range, even if you have turned invisible(Shade's Ghost etc)
- Ironically, Toxic Ancients can be hurt by Poison Damage.
- If Sentinels are used in missions, be cautious, as the fumes created by the Toxic Ancients cause significant damage to them.
- After the change in model and appearance in update 9, their lower legs are very hard to hit, as bullets will usually miss or go through the legs without dealing damage. Try to aim between the middle of the legs and their "waist" as most bullets will hit this area.
- It is not recommended to use Mag's Pull against this target.
- Using Nekros' Soul Punch will send an ancient flying which can be very helpful on high level defence
- Standing in the poison cloud while Trinity's Link is active will cause damage to linked enemies.
- When in a subtle state (not in alert), Toxic Ancients do not emit toxic fumes out of their bodies.