Just launched is the Hunter / Prey expansion alongside the massive 2.9 update. Hunter/Prey adds in lots of new units and buildings and I'll explain in detail their roles and some tips and tricks to using them. Overall, most of the new content is niche and situational compared to the existing content. This was to deliberate to ensure the new content opened up new and widened strategic options instead of overlapping with old stuff.

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New Substrate Structures

Auxiliary Assembly

This new building produces all of the new units, except for the Heart of the Phoenix, which can be built in the Advanced Assembly. Aside from the Scarabs, each new cruiser requires a tech building to unlock.

New Substrate Units

Scarab

Video showcase:
Overview: A heavy frigate squadron that is slow but tough and with heavy firepower. 
Role: Heavy Frigate

Tips for Scarabs:

• While very cost-effective, Scarabs can be easily outmaneuvered so attack your opponent's resources where the fight can't be avoided.
• Scarabs move at almost half the speed of other frigates and cruisers. Don't mix Scarabs in as armies to existing units, else you'll bog the whole army. Scarabs work best on their own with some anti-air support.

Tips against Scarabs:

• Scarabs get devastated by area of effect attacks such as the Hades Bombers.
• Use scout planes and radar to see incoming attacks. Scarabs are so slow that you can prepare static defenses by the time they arrive.

Skirmisher 

Overview: A fast-moving raider with weak durability for its cost but packs good damage.  
Role: Harassment Cruiser

Tips for Skirmisher:

• Use to avoid enemy forces and rush past defenses to harass enemy economy and infrastructure.
• Skirmishers are fast enough and with decent shield regeneration that they can simply disengage from a fight and move elsewhere
• Skirmishers can easily dodge incoming artillery projectiles if they change course, use them to punish Artillery.

Tips against Skirmisher::

• Rather than defending specific resource points, place static defenses in the choke points that Skirmishers would try to sneak past
• Skirmishers are weak in a direct fight for their cost, go on the offensive to deny your opponent fighting on their terms.
• Use gunships to quickly kill Skirmishers from the sky, Skirmishers are too fast for anti-air support.
• Avoid trying to use bombers like the Hades that are likely to miss the fast-moving Skirmishers.

Falling Star

Video showcase: 

Overview: A portable EMP bomb; when destroyed the Falling Star disables all nearby defenses for a short duration.

Role: Disruption Cruiser

Tips for Falling Star:

• Base defenses target units based on proximity (after initial unit type priorities), ensure a Falling Star is in the front of an assault.
• Falling Stars have high shield regeneration, don't be afraid to wait for it to regenerate before commencing an assault.
• The Destroy unit command can be used to manually detonate the Falling Star, this can be invaluable when the Falling Star is not being targeted and its disabling effect is needed.
• The Nano-Mesh barrier orbital can be used to give +2000 HP to the Falling Star, giving it more time to get into the perfect position to detonate.

Tips against Falling Star:

• Don't over-invest in base defenses, Falling Stars are practically worthless against units.
• Spread out your defenses so they're not all caught in the blast radius.
• Try to use longer range defenses with high burst (like the Oblivion) instead of shorter range, gradual damage towers like the Barrager.
• Stasis Hammers can prevent the Falling Star from getting within range.

Clutch of Eggs 

Video showcase:

Overview: A heavy walking spiderbot, when destroyed releases 16 powerful hatchlings (Frigates).

Role: Swarm cruiser

Tips for Clutch Of Eggs:

• The Clutch is weak for its heavy cost, but its real power comes in the hatchlings. Use them to overwhelm units and defenses with long reloads that lack AOE, such as the Minos Cannons, Eradicators and Athenas/Maulers.

Tips against Clutch Of Eggs:

• Make sure to mix in anti-frigate firepower such as Zeus, Masochists, Drone Bays and Disruptor Towers. 
• If completely caught off guard, the Plasma Storm and Drone Swarm orbitals are deadly against the Hatchlings.

Heart of the Phoenix

Video showcase: 
Overview: Versatile juggernaut that when destroyed it forms a Chrysalis that given enough time will regenerate and rebirth a new Phoenix.

Role: Endurance and disruption Juggernaut

Weaponry: Several missile swarms capable of engaging all targets, Static Charge which disables nearby units. Respawns at ~30% total health/shields if the Chrysalis survives for 30 seconds. (game time.)

Tips for Heart of the Phoenix::

• The Phoenix is versatile against all unit types but doesn't excel against any. It's a good investment if you don't know your opponent's strategy.
• Multiple Static Charges can stack and disable units for a long time, consider investing in multiple Phoenix's rather than mixing different Juggernauts together.
• Multiple Static Charges (Including from the Overmind) will especially synergize with keeping the Phoenix Chrysalis long enough to respawn.
• The Phoenix can be manually killed with the destroy unit command to turn into a Chrysalis. Though this will unlikely be useful as it loses combat levels and only respawns at ~30% total health.

Tips against Heart of the Phoenix:

• The Phoenix does not have the same firepower as other Juggernauts, duel it with a Leonidas or Eye of Darkness.
• While the Phoenix can devastate air units, it is with the same weapons as its ground attacks. Don't be afraid to combine an air and ground assault, but don't send the air in too early.
• The Phoenix lacks any splash damage, send in light units.
• Make sure to focus the Phoenix's chrysalis down before it can respawn.

New PHC Defenses

All new defenses (except for Minos Cannon) are tier 2 or tier 3 that upgrade from existing towers. Alternatively, they can be built directly on the map from the Sapper orbital abilities which summons an advanced engineer.

Shotgun Turret 

Overview: Very short-range turret but delivers massive damage.

Upgrades from: Emergency Turret (Orbital Ability)

Tips for Shotgun Turret:

• Invest in the Shotgun Turret over the MachineGun when you know the enemy has a large amount of short-range units such as the Athena and Mauler.
• The Shotgun excels in overlooking a high ground position where enemies will not be able to shoot up without vision.
• The cost of spawning Emergency Turrets will increase throughout the game. Use the Sapper to build more Shotgun and Machine Gun Turrets with a fixed Quanta cost.

Tips against Shotgun Turret:

• The shotgun can simply be outranged by a medium-range enemy like the Nemesis. Utilizing the Hold Ground unit command may charge your units from charging within range of the Shotgun Turret.
• The shotgun excels against cruisers, with its 1 second reload it can struggle against swarms of frigates.

Machine Gun Turret

Overview: Versatile damage and medium-range. Can target both ground and air targets.

Upgrades from: Emergency Turret (Orbital Ability)

Tips for Machine Gun Turret:

• Use when the short-range of the Shotgun tower will be limiting or when additional anti-air firepower is needed.

Tips Against Machine Gun Turret:

• The Machine Gun Turret has no particular weaknesses, sieging it with an Artillery cruiser may be necessary unless you have an overwhelming force.

Kinetic Accelerator

Overview: Provides a 20% damage boost to all nearby weapons. 

Upgrades from: Sensor Post

Tips for Kinetic Accelerator:

• Don't invest in one too early. 20% bonus is not significant for only a handful of Smarties.
• Selecting the Kinetic Accelerator tower shows you its buff range (1000). Use this as a reference.
• The Kinetic Accelerator is extremely fragile, place it behind other defenses so it is protected.
• If you can, leapfrog Battery towers forwards and try to fight near them. You may have to lure enemies into engage you in the buff range.
• Its selection range of 1000 indicates its buff range, but the Kinetic Accelerator still provides 3000 radar range. You don't need to rebuild a Sensor Array.

Tips against Kinetic Accelerator:

• The Kinetic Accelerator is extremely fragile at 300 health. Take it out with a Sentries, Saboteur, Incursion Drone Swarm, Plasma Storm before an engagement.
• If Orbital jamming is present, suicide a bomber or two to destroy it before an engagement.

Nova Tower 

Video Showcase: 
Overview: Indirect bombardment weapon that delivers heavy shield damage in a wide area-of-effect at.

Upgrades from: Artillery Post

Tips for Nova Tower:

• Deals no physical damage so it is useless against PHC. Though, it will only ever fire at shielded enemies
• Best used to support Artillery Posts or prior to assaulting an enemy position. 
• Use Sensor Posts (Or Kinetic Accelerator) to reveal targets.

Tips against Nova Tower:

• The shield damage can be counteracted by mixing in Caregivers and Regenerators.
• The Nova Tower, like the Artillery Post, is extremely weak. They can be quickly destroyed by bombers.

Stasis Hammer

Video showcase:
Overview: Deals no damage but stuns an enemy in place for a few seconds.

Upgrades from: Sentinel Cannon

Tips for Stasis Hammer:

• The Stasis Hammer can stun cruisers but it's likely only a worthwhile investment against Dreadnoughts and Juggernauts.
• Multiple Stasis Hammer stuns stack, don't be afraid to invest in a few.

Tips against Stasis Hammer:

• The Stasis Hammer is moderately fragile at only 2000 health. Consider focusing it down first, bombers or otherwise.
• Artillery units will be able to siege the Stasis hammer with no risk, unless there are nearby Artillery Posts.
• Unless it is well-supported, Stasis hammers can be overwhelmed with light units.

Minos Cannon

Video showcase:
Overview: Tier 3 anti-dreadnought and anti-juggernaut defense. Fires 6 devastating armor-piercing shots in a rapid burst over long-range.

Tips for Minos Cannon:

• The Minos Cannon's long reload and slow turret rotation leave the Minos Cannon vulnerable to swarms of light units. Make sure to other types of base defenses to complement that weakness. In particular, Drone Bays devastate frigates and the Hatchlings from the Clutch Of Eggs.
• Mix with a Battery Tower and Stasis Hammer for additional effect
• The Minos Cannon has more attack range than sight range, mix in a Sensor Array (Or Kinetic Accelerator) to ensure it's firing at max range.

Tips against Minos Cannon:

• A dreadnought charge against a Minos Cannon is suicidal, don't attempt this. Even a Juggernaut charge may fail if well fortified or multiple Minos Cannons are present.
• If your opponent is heavily entrenched, it's possible you can flank their defensive position and attack elsewhere such as their economy or Nexus. Supported Minos Cannons are a massive investment.
• For PHC - Use the Cronus artillery dreadnought to outrange the Minos Cannon from a distance safely.
• For Substrate - Mass Clutch Of Eggs or other frigates can easily overwhelm a Minos Cannon, even mass cruisers can do the job. 
• Substrate - Use Mix in Falling Stars to disable the Minos and other supporting defenses.
• Substrate - Tormentor artillery frigates have more range than Destructors and will be able to safely outrange the Minos Cannon, though they will take some time to chip away at it.