"The optimization of weapons, armor, and ships is a phase-smith's highest calling, and Karax is one of the most precise engineers in the whole of the Khalai. He rose above his station in the protoss' worker caste to become a crucial asset in Artanis's war against Amon, earning the title of templar and causing Artanis to declare the end to the age of castes. As the Phase-smith responsible for restoring the Spear of Adun's systems, Karax is intimately familiar with the Arkship's suite of destructive weaponry. During his time with Artanis, Karax also recovered some of the Purifier-based weapon systems which you'll find in his Co-op Mission arsenal."
Karax is a playable commander in the Co-op Missions, added in patch 3.1. He utilizes an array of advanced protoss weaponry and Purifier-type units to yield an army of robotic attackers, and has access to the Solar forge, which can be upgraded to enhance the Spear of Adun's abilities.
Upgrades colossus to purifier colossus and unlocks the following upgrades at the robotics bay. • Unlock the immortal's Shadow Cannon ability, which deals 200 damage to an enemy ground or air unit. • Enable the colossus's attacks to set fire to the ground for additional damage over time.
All of Karax's combat units have a 30% increase in their resource costs, but fully upgraded they are very effective. He is overall more of a support commander, using his chrono abilities to improve production times for him and his allies, building static defenses to defend points of control, and utilizing the Spear of Adun's powers to attack from afar. However, he is still perfectly capable of fielding a powerful army if required.
Power Set 1:
Structure Life and Shields allows cannons (240 shield + 240 hp total) to survive one Yamato cannon shot from Terrans. Its is useful when you plan to play extremely defensively and rely on static defense as your primary strategy, which can be viable on defensive maps and certain mutations.
Power Set 2: Both options are equally viable.
☀Repair Beam Healing Rate: (+1% - +30%)
☀Chrono Wave Energy Generation (+1 - +30)
Chrono Wave Energy Generation allows you to save resources on Solar Efficiency upgrades, and the superior choice for a mass Carrier composition. A static defense build can better afford the gas for Solar Efficiency upgrades, making the Chrono Wave Energy Generation less of a relative improvement.
Repair Beam Healing Rate equates to better healing for both tower defence and army-based strategy. Sentinels and Mirages are much tougher; static defenses have better chances to withstand enemy attacks, indirectly increasing the ability to survive under certain mutations.
Power Set 3: Initial and Maximum Spear of Adun Energy
☀Initial and Maximum Spear of Adun Energy: (+3 - +90)
Initial and Maximum Spear of Adun Energy allows for -immediate- expansion; significantly increases Karax’s early game power. This energy can be spent in many different ways, but most notably giving Karax the fastest possible expansion of any commander on all maps. Should you research multiple Solar Efficiency upgrades, being able to store an extra 90 energy can allow you more freedom to bank your energy, and can provide you with extra burst damage which you will need in the late game.
Chrono Boost Efficiency has niche uses and is made redundant by Chrono Wave.
The solar forge provides bonus energy to the Spear of Adun, which powers many of Karax's abilities. The first upgrade at the forge will increase the amount of bonus energy supplied, enabling Karax to use the powerful abilities which the Spear of Adun provides more often. Chrono wave is an incredibly powerful ability. Before using it, consider informing one's fellow player of the intention to use it. This will allow them to start upgrades, queue units, and generally ensure that both of you receive the massive benefits that the ability is capable of providing. Orbital strike can provide quick support to one's ally.
Use the Energizers to "mind control" Terran/Protoss mechanical units, particularly expensive units such as carriers or battlecruisers. Create a mixed force of Immortals/Carriers to supplement [Sentinels/Photon Cannons with the remaining minerals.
Karax's strength is about researching technology, aiding partners with spells and deploying static defense: you have the strongest hero powers by far and the strongest static defense by a significant margin. The drawback is that his standing army is pitifully small. Even when only investing in spells and carriers, for example, you'll only have 8~10 carriers at the end of the game; and the strong feeling that Karax was carried by his ally. Because his units cost 30% more, you shouldn't play Karax like you play any other hero. The first 10 minutes of the game, Karax only has "token defense force"; only at the 15 minute mark will production "ramp up".
Despite Karax's slow ramp up while levelling(offset by the recent buffs to his unit costs), he can be a truly terrifying fighting force with masteries. His zealot variant, the sentinels, can revive themselves and is effectively two zealots for the price of one. His energizers have the ability to take control of powerful enemy mechs and increase friendly units' attack speeds. His immortals' shadow cannon ability can deal impressive damage to single targets from extremely long range. With army cost reduction mastery and precise Orbital Strikes, Karax's army is extremely cost efficient and powerful.
A key aspect of Karax mastery is the usage of his Spear of Adun orbital strike ability and its synergies with Karax's army. Orbital strikes take time to land, so it is important to lead your shots against moving enemy waves. To maximize the damage of orbital strikes, aim for clumped armoured enemies, such as air units over structures, or units forced to group up while turning or crossing chokes, for the bonus damage to apply. Against certain enemy compositions, it is advisable to research the orbital strike stun upgrade: when attacking into fortified enemy positions, target dangerous enemies like capital ships and spellcasters to stop them from firing; when against an incoming air attack wave, time your shots so that you can stun the front of the attack wave, allow the back of the wave to get close to the already stunned parts of the wave, then fire to stun and damage even more units as they clump up. It is also important to not pointlessly spam your shots against single targets: your units and static defenses will do fine against those. Knowing how many shots it takes kill different units will also help you efficiently use your orbital strikes: spam clicking against a battlecruiser fleet is pointless when six well-placed shots can stun and destroy them anyway. In addition, you can also combo orbital strikes with your other units: normally it takes three shots to kill a broodlord or a void ray, but with an immortal shadow cannon, one shot is enough; sentinels act as good tanks, but more importantly, they aggro enemy units and force them to stay close, allowing you to target them easily.
Raynor synergizes only decently with Karax; Raynor can produce multiple barracks to quickly rebuild his army and thus won't be helped as much by Chrono Wave. Reconstruction Beam may not affect Raynor's infantry, but it can help his mechanized units and bunkers, the latter of which normally have survivability issues at higher difficulties. Vikings and marines can help Karax compensate for his lackluster anti-air capabilities.
Swann synergizes perfectly when paired with Karax, due to both commanders' focus on mechanical units. Karax's powerful anti-ground forces with the immortal and colossus are well complemented by Swann's powerful anti-air goliath and thor. Swann's science vessels and Karax's carriers can repair mechanical units, and both can combine their static defenses together for more versatility. Karax is incredibly gas starved, and Swann goes a long way to alleviate this. This is the only way to obtain a true army of powerful units for Karax. Karax's passive heal of mechanical units comes in extremely handy in the early game; Swann's units are as strong as they are slow, making it more difficult for Swann to retreat in battle. Karax's reconstruction beam ability is particularly useful in this case. If all else fails and both players suffer great losses in battle, Karax can help both players recreate their armies faster than anyone else.
Nova is an effective teammate for Karax. Her lack of defensive systems is covered by Karax's strong statics, while Nova can handle bases and attack points on her own. Since Chrono-Boost and Chrono-Wave quickens not only her research time but also the cooldown of her facilities, Nova gets a great advantage of quickly replacing units if needed and also being more "selectable" with which kinds of units she want.
Han and Horner work amazingly well with Karax. Han and Horner lack any true reliable defensive structures on maps like “Temple of the Past” and “Dead of Night,” having to rely on widow mines and mag mines. Karax can cover for this, and meanwhile their mag mines can provide extra support for Karax's defenses, hitting targets while they're tied up dealing with his photon cannons. Reconstruction Beam also is a powerful boon to Han and Horner, as it gives their assault galleons a reliable heal while increasing the repair rate of their more powerful Horner units. Strike fighters also can reveal areas in the fog of war, allowing Karax to them hit targets with his orbital abilities. Chronoboost is a massive boon to Han and Horner, who have a lot of research that is of great benefit to their armies. Han and Horner can field a big army with heavy pushing potential, and their larger units gain a lot of benefit from energizers. Karax's Aiur carriers can bolster the already impressive tanking potential of Horner's fleet as well as somewhat increasing the survivability of hellions and widow mines. When combined with drone hangar assault galleons they can deal a significant amount of damage from out of enemy range.
Tychushas reasonable synergy with Karax. While he can't take advantage of Chrono Wave as his research and training times are nonexistent for the most part, the power of the Heaven's Devils helps offset Karax's slow ramp-up time. In return, Karax covers for Tychus's weak defensive abilities and can provide covering fire for the Devils with the Spear of Adun's calldowns, while buffing them with Energizers.
Kerrigan has access to mutalisks and ultralisks; units that take a long time to create, and would benefit greatly from Karax's chrono-boost ability.
Zagara already creates units quickly due to her relentless swarmer trait, but she can still benefit from Chrono Wave for research and upgrades. Unity Barrier can make her frail units slightly more durable, and Karax can cover for Zagara's lackluster base defenses.
Abathur has some ability synergies with Karax, as his chrono wave can boost his research and production, which is essential to Abathur's army strength. Toxic nests work well with Karax's static defenses, and the Spear of Adun's orbital bombardment abilities can help cover Abathur from air units in the early game.
Stukov works well with Karax, particularly on defensive maps. When pushing forward, the two can create small "checkpoints" of structures as Stukov moves his production buildings up and Karax covers them with defensive structures. Stukov's infest structure synergizes well with the amount of defenses Karax has, and Chrono Wave can boost the speed of long upgrades for Stukov such as the infestation levels. Both Karax and Stukov have powerful global cooldowns, with Karax's more consistent orbital strike and solar lance abilities allowing Stukov to save his Apocalisk and Aleksander for more important engagements.
Dehaka and Karax have situational synergy. On defensive maps like “Temple of the Past” and “Night of the Dead”, Karax can cover for Dehaka's lack of reliable defensive structures while Dehaka pushes out for other objectives. Meanwhile, Karax can cover for Dehaka with his offensive calldowns. However, Karax's repair beam does not benefit Dehaka as he has no mechanical units, and on maps that rely heavily on pushing Karax is unable to reliably support Dehaka in the mid game.
Artanis synergizes well with Karax. Reconstruction beam can heal units saved by Guardian Shell, making both players' units nigh-unkillable. Karax's plentiful energy on the Spear of Adun means Artanis can save gas on expensive Protoss artillery and use his strong basic units (immortal, archon, dragoon, phoenix), and Chrono Wave can ensure both players are well-upgraded (particularly on weapons and shields).
Vorazun benefits from Chrono Wave if she is building an air force or rebuilding an army, as dark templars and dark archons have a long cooldown on warp gates. She also benefits from Chrono Wave in her tech, as she needs to research many upgrades to reach full power. Her Vortex can also bunch up the enemy for Karax's Orbital Strikes and Solar Lances. Her Dark Pylon can also cloak Karax's defensive structures, making them much more effective.
Alarak is a moderately effective teammate for Karax. While Alarak is geared towards overwhelming offense, Karax favors impenetrable defense. Thus Alarak can focus his attention on attacking the enemy while Karax defends their bases and uses his calldown abilities to focus down stronger units Alarak may have trouble with. Reconstruction Beam is invaluable to support Alarak's fragile wrathwalkers and vanguards, and carriers with repair drones makes a powerful army combined with Alarak's robotic forces. The player can use Alarak's Structure Overcharge to power up Karax's defenses even further when faced with an overwhelming enemy force.
Fenix is a very effective teammate for Karax. As all of Fenix's units are mechanical, he benefits greatly from reconstruction beam, allowing his entire army to be more durable. Fenix also lacks defensive options while Karax lacks offensive options, making the two good on push-pull maps. Fenix can also defend early using his heroes while Karax establishes a defensive line, allowing Fenix to hit a critical mass. The only downside is both heroes are not the best at pushing, though Fenix gains a lot of push potential with Karax's heal and shield batteries, and Karax will have to be on top of supporting Fenix with his Spear of Adun abilities in order to get past some of the tougher fortifications without Fenix taking too much damage.