In previous editions of D&D it was possible to have two base forms or (in some editions) a creature 'template'. In 5e the base form is important and always singular: many spells &/or magics only work on specific creature type(s). The problem we encountered: can a Simulacrum be Reincarnated? You will note that the Simulacrum specifies that it can only be cast on humanoids and the spell claims it creates an exact duplicate. That said, this exact duplicate cannot accept healing &/or learning. What's more, this replicant has only half the hit points.
With Reincarnation you will note that the recipient creature must be a humanoid. Previous editions were much more open to include many other living creatures but 5e is very specific. Thus, this spell will allow the reincarnation of exotic creatures such as Xvarts, half-dragon kobolds or even Nagpas - but not any beast, giant, or fae, regardless of how identical they are to humans. But i digress. The long and short of this: a construct will NOT be reincarnated. It is devoid of the life required to incarnate in the first place (in fact, it is odd that a construct is considered a 'creature' and not a 'magic item').
What is odd about D&D constructs, they are far more alive than most people. They heal after a short or long rest. The Simulacrum does not get this. Many a construct (or animated dead) does not suffer exhaustion - but a Simulacrum does.
In previous editions of D&D (particularly 3.x), creatures were strongly typed and those types had meaning to them. A creature of type construct always had properties A, B, and C; while a creature of type undead always properties Q, R, S, and T, and so on.
In D&D5E, that same kind of strong typing and implicit abilities does not exist. Other than being used as a flag in other things (like spells requiring a humanoid target, as you've discovered) the types have no inherent properties. One should not take one particular construct exhibiting certain abilities as all constructs exhibiting those abilities. Each creature needs to be looked at individually.
A humanoid usually has two arms, two legs, and one head, or a humanlike torso, arms, and a head. Humanoids have few or no supernatural or extraordinary abilities, but most can speak and usually have well-developed societies. They usually are Small or Medium. Every humanoid creature also has a subtype.
An outsider is at least partially composed of the essence (but not necessarily the material) of some plane other than the Material Plane. Some creatures start out as some other type and become outsiders when they attain a higher (or lower) state of spiritual existence.
This type comprises vegetable creatures. Note that regular plants, such as one finds growing in gardens and fields, lack Wisdom and Charisma scores (see Nonabilities) and are not creatures, but objects, even though they are alive.
These creatures always have swim speeds and thus can move in water without making Swim checks. An aquatic creature can breathe underwater. It cannot also breathe air unless it has the amphibious special quality.
A subtype usually applied only to outsiders native to the chaotic-aligned Outer Planes. Most creatures that have this subtype also have chaotic alignments; however, if their alignments change they still retain the subtype. Any effect that depends on alignment affects a creature with this subtype as if the creature has a chaotic alignment, no matter what its alignment actually is. The creature also suffers effects according to its actual alignment. A creature with the chaotic subtype overcomes damage reduction as if its natural weapons and any weapons it wields were chaotic-aligned (see Damage Reduction, below).
A creature with the cold subtype has immunity to cold. It has vulnerability to fire, which means it takes half again as much (+50%) damage as normal from fire, regardless of whether a saving throw is allowed, or if the save is a success or failure.
This subtype usually is used for elementals and outsiders with a connection to the Elemental Plane of Earth. Earth creatures usually have burrow speeds, and most earth creatures can burrow through solid rock.
A subtype usually applied only to outsiders native to the evil-aligned Outer Planes. Evil outsiders are also called fiends. Most creatures that have this subtype also have evil alignments; however, if their alignments change, they still retain the subtype. Any effect that depends on alignment affects a creature with this subtype as if the creature has an evil alignment, no matter what its alignment actually is. The creature also suffers effects according to its actual alignment. A creature with the evil subtype overcomes damage reduction as if its natural weapons and any weapons it wields were evil-aligned (see Damage Reduction, above).
A subtype applied to any creature when it is on a plane other than its native plane. A creature that travels the planes can gain or lose this subtype as it goes from plane to plane. Monster entries assume that encounters with creatures take place on the Material Plane, and every creature whose native plane is not the Material Plane has the extraplanar subtype (but would not have when on its home plane). Every extraplanar creature in this book has a home plane mentioned in its description. Creatures not labeled as extraplanar are natives of the Material Plane, and they gain the extraplanar subtype if they leave the Material Plane. No creature has the extraplanar subtype when it is on a transitive plane, such as the Astral Plane, the Ethereal Plane, and the Plane of Shadow.
A creature with the fire subtype has immunity to fire. It has vulnerability to cold, which means it takes half again as much (+50%) damage as normal from cold, regardless of whether a saving throw is allowed, or if the save is a success or failure.
A subtype usually applied only to outsiders native to the good-aligned Outer Planes. Most creatures that have this subtype also have good alignments; however, if their alignments change, they still retain the subtype. Any effect that depends on alignment affects a creature with this subtype as if the creature has a good alignment, no matter what its alignment actually is. The creature also suffers effects according to its actual alignment. A creature with the good subtype overcomes damage reduction as if its natural weapons and any weapons it wields were good-aligned (see Damage Reduction, above).
An incorporeal creature has no physical body. It can be harmed only by other incorporeal creatures, magic weapons or creatures that strike as magic weapons, and spells, spell-like abilities, or supernatural abilities. It is immune to all nonmagical attack forms. Even when hit by spells or magic weapons, it has a 50% chance to ignore any damage from a corporeal source (except for positive energy, negative energy, force effects such as magic missile, or attacks made with ghost touch weapons). Although it is not a magical attack, holy water can affect incorporeal undead, but a hit with holy water has a 50% chance of not affecting an incorporeal creature.
A subtype usually applied only to outsiders native to the lawful-aligned Outer Planes. Most creatures that have this subtype also have lawful alignments; however, if their alignments change, they still retain the subtype. Any effect that depends on alignment affects a creature with this subtype as if the creature has a lawful alignment, no matter what its alignment actually is. The creature also suffers effects according to its actual alignment. A creature with the lawful subtype overcomes damage reduction as if its natural weapons and any weapons it wields were lawful-aligned (see Damage Reduction, above).
A shapechanger has the supernatural ability to assume one or more alternate forms. Many magical effects allow some kind of shape shifting, and not every creature that can change shape has the shapechanger subtype.
A swarm of Tiny creatures consists of 300 nonflying creatures or 1,000 flying creatures. A swarm of Diminutive creatures consists of 1,500 nonflying creatures or 5,000 flying creatures. A swarm of Fine creatures consists of 10,000 creatures, whether they are flying or not. Swarms of nonflying creatures include many more creatures than could normally fit in a 10-foot square based on their normal space, because creatures in a swarm are packed tightly together and generally crawl over each other and their prey when moving or attacking. Larger swarms are represented by multiples of single swarms. The area occupied by a large swarm is completely shapeable, though the swarm usually remains in contiguous squares.
A swarm has no clear front or back and no discernable anatomy, so it is not subject to critical hits or flanking. A swarm made up of Tiny creatures takes half damage from slashing and piercing weapons. A swarm composed of Fine or Diminutive creatures is immune to all weapon damage. Reducing a swarm to 0 hit points or lower causes it to break up, though damage taken until that point does not degrade its ability to attack or resist attack. Swarms are never staggered or reduced to a dying state by damage. Also, they cannot be tripped, grappled, or bull rushed, and they cannot grapple an opponent.
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