I'm playing an artificer (from Unearthed Arcana) and he just reached level 6, unlocking the Mechanical Servant feature. I was looking around for some CR 2 large beasts and I found the Plesiosaurus. It has the Hold Breath trait, which allows it to hold its breath for an hour. This got me thinking about whether or not constructs need air, or more specifically, whether or not the mechanical servant needs air.
The Mechanical Servant feature says:
Select a Large beast with a challenge rating of 2 or less. The servant uses that beast’s game statistics, but it can look however you like, as long as its form is appropriate for its statistics. It has the following modifications:
It is a construct instead of a beast.
It can’t be charmed.
It is immune to poison damage and the poisoned condition.
It gains darkvision with a range of 60 feet if it doesn’t have it already.
It understands the languages you can speak when you create it, but it can’t speak.
If you are the target of a melee attack and the servant is within 5 feet of the attacker, you can use your reaction to command the servant to respond, using its reaction to make a melee attack against the attacker.
It says nothing about the servant being able to survive without air, but realistically speaking a robot doesn't need air.
Do constructs need air to survive?
Best Answer
Unless the particular construct is described as not needing air - it needs air
In the Monster Manual p.6 it says:
However, that is a feature of the particular "spells, magic items, class features, and other effects" on constructs - it is not inherent in constructs themselves.
Constructed Nature
Some constructs have this feature but it is far from universal:
So that is a feature of [X] in particular, not constructs in general.
Artificer
As currently written, the mechanical servant does not get Constructed Nature, so it needs air, food, drink and sleep.
Hence: