Mechanoid hive

Mechanoids - Autonomous intelligent robots built for domestic, industrial or military purposes. Only available to advanced cultures because such complex AI is needed to control them.
— RimWorld Universe Quick Primer

A Mechanoid Hive is a permanently hostile faction composed entirely of mechanoids, deadly autonomously intelligent robots.

Summary

All mechanoids from a mech hive are permanently hostile to the colony. They do not eat and are immune to toxic fallout and temperature extremes, despite having a Comfortable Temperature range. As machines, they are vulnerable to EMP attacks, though will "Adapt" for 2,200 ticks (36.67 secs) (regardless of source), making them immune to all further EMP strikes. Hostile mechanoids do not fear for their life, unable to feel pain and will not seek to take cover.

Mechanoids can be found sealed in ancient ruins in all biomes, which spawn inside mountains or outside on the landscape. They may also raid the player's base through events and can also be found in most poison ships, psychic ships, and mech clusters. They may sometimes appear dormant in Ancient Complex and guarding any relic with Ideology DLC.

Hostile mechanoids are not bound by power limits. While mechanitors can create their own allied mechanoids in the Biotech DLC , they are unable to tame or convert hostile ones. Friendly mechs may become feral and join a mech hive if left Uncontrolled (such as having too little bandwidth) for too long, and can't be re-converted.

Pawns

Pawn Groups

Pawn Groups	Commonality	Options
Combat: All types	100	15.6% Scyther 15.6% Pikeman 15.6% Lancer 15.6% Centipede blaster 31.3% Militor 3.1% Centurion 1.6% War queen 1.6% Apocriton
Combat: Ranged only	80	30.3% Pikeman 30.3% Lancer 15.2% Scorcher 15.2% Tesseron 6.1% Legionary 3% Diabolus
Combat: Melee only	70	100% Scyther
Combat: Centipede only	30	50% Centipede blaster 25% Centipede gunner 25% Centipede burner
Combat: militor only	30	100% Militor
Combat: breach raids	1	16.4% Pikeman 16.4% Scyther 16.4% Lancer 16.4% Centipede blaster 1.6% Termite 32.8% Militor

Pawn Kinds

Pawn Type	Combat Power	Armor (S/B/H)	Weapons	Age Range	Move Speed	Additional Info
Scyther	150	40% / 20% / 200%	Melee (Blades)	Any	4.7 c/s	-
Lancer	180	40% / 20% / 200%	Charge lance	Any	4.7 c/s	-
Centipede blaster	400	72% / 22% / 200%	Heavy charge blaster	Any	1.9 c/s	-
Centipede burner	400	72% / 22% / 200%	Inferno cannon	Any	1.9 c/s	-
Centipede gunner	400	72% / 22% / 200%	Minigun	Any	1.9 c/s	-
Pikeman	110	40% / 20% / 200%	Needle gun	Any	2.5 c/s	-
Termite	110	56% / 22% / 200%	Thump cannon	Any	2.1 c/s	-
Militor	45	20% / 10% / 200%	mini-shotgun	Any	3.8 c/s	-
Legionary	150	40% / 20% / 200%	Needle launcher	Any	4.3 c/s	AoE shield
Tesseron	150	40% / 20% / 200%	Beam graser	Any	4.7 c/s	-
Scorcher	75	40% / 20% / 200%	Mini-flameblaster	Any	4.5 c/s	-
Tunneler	250	80% / 40% / 200%	Melee (Power claws)	Any	1.9 c/s	Personal shield
Centurion	250	75% / 25% / 200%	Charge blaster turret	Any	1.6 c/s	AoE shield
Diabolus	500	75% / 25% / 200%	Hellsphere cannon	Any	2.4 c/s	Flame burst ability
War queen	600	75% / 25% / 200%	Charge blaster turret	Any	1.6 c/s	Produces war urchins
Apocriton	600	75% / 40% / 200%	Toxic needle gun	Any	3.2 c/s	Various^{[Add these]}
War urchin	10	20% / 10% / 200%	Spiner	Any	4.2 c/s	-

Analysis

Mechanoid forces are specialized by their unit types, with each unit performing a single role. Basics summaries are available here, see the individual pages for further details and analysis.

Scyther - The melee boogeymen of Mechanoids. Fast and extremely dangerous up close, large numbers can and will overwhelm single enemies. Melee blocking, use of chokepoints, and focus fire while they close in are useful tactics. Mechanoid raids consisting entirely of large numbers of scythers are fairly common.
Lancer- Armed with charge lances, they have medium range and modest overall DPS. However, their high shot damage presents a modest, but serious risk of one-shot-killing pawns by destroying body parts. Therefore, exposure should be limited and lancers prioritized as threats. Like many non-scythers, melee combat is very effective if a pawn can get close enough.
Pikeman - Acting as the sniper, their needle gun doesn't do too much damage. Their main role is to allow mechanoids to engage at range - use bends in chokepoints to force them into range, or simply advance and kill them.
Centipede - Centipedes are tanks and crowd controllers. They are incredibly durable, but rather slow. They can wield heavy charge blasters or miniguns for raw, inaccurate damage, or inferno cannons to light fires and force ignited pawns out of cover. Mortar Fire and melee combat are decent options for actually damaging the centipede due to it's slow movement speed and large size, and avoid bunching against any of their weapons. Alternatively, a psychic insanity lance against a centipede turns a danger into a significant asset, though note that other mechanoids are immune to inferno cannons.
Termite - While not particularly dangerous on their own, their thump cannon can destroy most walls in a single shot, leaving your colonists open to damage from other mechanoids. Depending on the exact strategy employed against the raid as a whole, these might be the highest priority, or of negligible concern.
Militor - A small combat mechanoid armed with a low power, 12 range mini-shotgun. One of the weakest mechanoids, they serve as earlygame threats and support other mechanoids. They can be scary through sheer numbers - large mechanoid raids comprised only of militors occasionally spawn.
Scorcher - A mechanoid that specializes in incendiary attacks. Its flame burst attack has little reach, but once it closes on a group of defenders it can ignite and disrupt them with blasts of searing flame.
Legionary - A combat support mechanoid with a wide range bullet shield and long-range needle gun. Designed to support other mechanoids from long range, the legionary is vulnerable to anyone who can get inside its shield.
Tesseron - A medium-range combat mechanoid. The tesseron's sweeping beam attack pierces shields, ignites pawns, and deals great damage, but can't be fired up close.
Centurion - An incredibly durable ultra-heavy mech, with a large shield capable of defending allies. It also has point-defense turret, which can fire while moving.
Tunneler - A large, somewhat durable melee mechanoid with a natural shield and smokepop. While mostly made for mining, some apocriton summon groups will arrive with tunnelers. Does not seem to appear in regular mech raids.
Diabolus - An ultra-heavy mechanoid with an ultra-powerful hellsphere cannon. It takes time to charge up, but devastates everything including buildings and walls in a large radius. Also has a flame burst for use against nearby foes, and a general purpose turret.
War queen - An ultra-heavy mech with a built-in mech gestator. Fed with appropriate resources, the war queen can form small war urchin combat mechs within its massive carapace and deploy them into combat.
Apocriton - A mechanoid commander designed to coordinate and motivate other mechs during long extermination campaigns. Its most obvious power is its ability to resurrect recently-killed mechs by supercharging their self-repair processes. Less obviously, it is intelligent and psychically present, radiating hatred into the minds of anyone in a wide radius. While all mechanoids have a dim psychically-present intelligence, only the apocriton and a few others truly feel hatred for their victims and understand the suffering they inflict.

Trivia

Although all mechanoid-only weapons are 'Spacer' in terms of tech level; the hidden mechanoid faction itself is actually 'Ultra' tech level - one above 'Spacer', and the second highest tech level in the game, below 'Transcendent'.