Support Arc Guide

### Introduction

This is an economy-focused build with a lot of diverts, exploration droids and other support structures. It's backed by an ability of an Arc Welder to double-mine together with a droid. You'd improve an economy for your allies by using accelerant drones, speed up the fueling by 5-10 minutes and help your team with scouting and tagging alphas. You'll do damage by setting up and maintaining turret nests.

### Build items

Let's start with a list of items to get eventually. The order and priority would be covered later and is quite flexible.

* Arc Welder (+ tier 2/3 upgrades)
	+ That's a core part of the build, enabling a double-mining and allowing to charge/repair turrets and other structures.
	+ It's an experimental but also a gun, meaning an appearance in the weapons section and a tier-like upgrade system.
	+ Upgrades aren't high-pri till the late game and may be skipped entirely in favor of other build components. Tier 2 can be acquired earlier if the tough defense is anticipated alone or with a handful of marines.
* Mining droid (+ 2 speed upgrades)
	+ An economic investment is essential for this build. Diverts, technology, support units/structures and turrets cost a lot.
* Stimpack
	+ Improves a marine mining speed by 35%.
* Accelerant Drone
	+ Improves mining speed of your marine and all droids on the mining path by 40% (at most 2 units at once).
	+ Arc charging and being around for mining makes their maintenance pretty easy.
* Exploration Droid Module (+ upgrade)
	+ A crucial part of this support build to provide early vision for teammates and tag alphas.
* Turrets
	+ That's your way to deal damage, as the arc weapon damage is puny.
	+ Get a couple of flame turrets early and/or versus mass lings.
	+ Get heavy turrets versus armored zombies, tier 3 strains and alphas.
	+ Get spec ops turrets as a supplement to flame turrets against low-hp zombies.
* Psi Disrupter (+ Psi Depressor upgrade)
	+ This helps to keep important rooms around your mining safe.
	+ Psi Disrupter in a hangar is crucial.
	+ Psi Depressor has a compounding effect on making the hold easier.
	+ Spec Ops Psi Disruptor is rarely worth it, maybe only when un-infesting a room. Extra security units just don't do that much against an even medium horde push and alphas.
* Caduceus Energy Suit (+ upgrade)
	+ Provides +2 charges of a security module (with an upgrade).
	+ Provides +1 charge of a mining equipment when coupled with the Quantum Backpack.
	+ Provides an extra energy regeneration, which may help repairing in long defenses.
* Medic Shield
	+ If mining in the sublevel, heals the periodic damage.
	+ Free healing of the Stimpack damage.
* Quantum Backpack
	+ Provides +1 charge of a security module.
	+ Provides +1 charge of a mining equipment when coupled with the Caduceus Energy Suit.
* AI Assistant
	+ Improves a marine mining speed by 5%.
	+ Helps to set up a hangar defense a bit faster.
* Mining charge
	+ Even though you'd be mining most of the time, pre-placing nukes in nearby critical locations can help future holds a lot.
	+ Important during hangar holds.
	+ The placement location should be a bit away from security units, as volatiles' AOE can take them down otherwise.
	+ Watch for nuke HP and pings from teammates, so you don't forget to blow it.
* Motion Sensor
	+ Multiple sensors around the mining area can help with zombie tracking later in the game, once exploration droids are used somewhere else.

### Build order

The items can be grouped by a priority. Within the same priority, the order would depend on circumstances. Even then, adjust the priorities if there's a need for that. Turrets is a notable example.

#### Starter pack

Get the Arc Welder and the Mining Droid. If zombie has an advantage, start with arc as marine's base movement speed is faster than the mining droid's one. As a micro-optimization, place the mining droid when you are at the mine for the same reason.

#### Turrets (unordered)

Get at least basic auto turrets once there's a big horde push coming your way and not enough teammates to defend. Get heavy turrets if there's a high risk of an alpha or a sunken cheese.

The turrets are way stronger when playing arc due to an easy recharge, repair and 100% salvage cost refund.

#### Exploration droids

Get them next and send to places around the Overmind room.

If there are any alphas eggs, send the droid near them ASAP and be ready to tag. Only get the exploration droid tagging upgrade after the droid is sent.

Keep (re)building droids until you have 3 (max).

#### Accelerant drones

These are an essential part of the economy due to their 40% speed boost to everyone on the mining line. Most or a whole mining line can be covered by 2-4 drones depending on the location. If there are many mining droids on the line, it can be worth adding extra accelerant drones, as each can only boost 2 units at the same time. For the same reason, don't have patrolling exploration droids near them.

#### Stimpack, Advance Droid Engines, Turbo Droid Engines, Medic Shield, AI Assistant

These boost the economy and are best to get ASAP.

The priority is Stimpack > Medic Shield > Advance Droid Engines, Turbo Droid Engines, AI Assistant. They are ordered by the amount of an economic boost (both Stimpack and droid speed upgrades provide +35% movement speed increase, but a marine's base movement speed is faster).

#### Psi Disrupter, Psi Depressor

Use these to fortify both regular and major rooms around your mining. They slow down the push and can also be the last bit needed for the room to stay alive.

Get the depressor upgrade after placing several disruptors.

#### Caduceus Energy Suit, Quantum Backpack, Mining charge, Motion Sensor, Spec Ops Bio-Mechanical Drone

The order depends on an in-game situation and a personal preference.

The suit and backpack are so late, since they aren't as valuable with little technology unlocked. They are good to get once you have some gas banked up and a technology ready to use.

Mining charges are usually inferior to the turrets when playing arc.

Sensor towers can be delayed due to having exploration droids (until they move to major rooms etc.)

Upgraded heal drones would be good for the hangar defense or the push into your mining. However, arc repair and juggling turrets with deconstruct/construct makes them not as important early.

#### Arc Welder tier 2 and tier 3

Yes, they are that late and only grabbed if there's an extra gas. They help with construction/deconstruction/repair/charge speed, but cost a lot. For example, extra 3 turrets and 3 healing drones would be more impactful.

All tier 3 upgrades can be useful. I recommend starting with an increased build and salvage speed to set up the hangar defense quickly. A time between the hangar opening and the zombie push there can be pretty short, so getting some turrets quickly is crucial. After the setup is done, switch to the faster charge/repair or the attack speed boost.

### Strategy

#### Diverting

With this build you can get 10-20 diverts in to speed up the fueling by 5-10+ minutes.

A good default point to start auto-diverts is after getting all economy-related upgrades. This sets up for enough money for both diverting and preparing a good defense in the end-game.

You can start as early as after the accelerant drones are set up, which would win a couple of extra minutes for fueling, but would leave you with little gas in the end game. Yes, despite double-mining you'd often be short on gas.

Put auto-divert on auto-cast, but also watch the cooldown. The reason is that auto-cast is not instantaneous and can be delayed until the next fuel deposit, elevator usage etc. Press D once it's ready.

#### Exploration droids and alpha tagging

Those provide a huge value to the team for early scouting, tagging alphas and keeping an eye on major rooms and the mining for cheeses.

Auto-mining means more micro time available to work with exploration droids. Extra economy means not delaying the core build much by paying for them.

Start with placing droids in the different part of the Overmind room or rooms around. Re-locate them later as a zombie captures more territory. Make sure to cover paths to mining and/or escape routes. Having droids in the major rooms can help against cheeses (e.g. zombie can send an Underseer to Power of Fuel and either spawn a Greater Nydus there or deep burrow the Abomination). This may be less relevant if alphas are tagged.

Now to the most important and rewarding part of using them - alpha tagging. The tag is there for 6 minutes, helping to stop/kill the alpha and prevent cheeses (if you tag an Underseer). Tagging all Underseers can be a crucial component of winning the game. Make sure to track their movement and ask teammates to hunt them down.

Once there's an egg, move one of the droids to it. Try to take a note on the time of the placement. Most eggs take 90 seconds to hatch, while the Underseer one takes 68 seconds. You can identify the type of the egg by its HP and a size. An Underseer egg is smaller and has 1500 HP. A tier 1 alpha egg has 2000 HP and a tier 2 alpha egg has 2500 HP. Tagging a tier 1 egg removes the tag once the alpha spawns (but not tier 2), so you'd have to tag the alpha as soon as it spawns. If you are a bit late, still try to walk the droid around in a case the alpha is still there. Zombies also regularly afk with their alphas for some time after spawning.

A minute after the egg spawned pay a very close attention to the droid, press E and be ready to tag. The time is short, as the alpha can start moving right away, e.g. an Underseer can escape to the sublevel. Also, with an Underseer vision the horde can kill the droid pretty fast. You can have more slack with a non-Underseer, but it can also deep tunnel etc. So overall, make tagging your top priority. If there's also a horde pushing your way, move away for safety. Tagging that Underseer is too important to miss.

Zombie can make tagging more complicated, e.g. putting an Underseer egg near a sublevel, building a sunken or having an Underseer around. If a zombie has vision, move the droid out of its range while waiting, and move in several seconds before the egg hatches. In many cases it would still be possible to get the tag. Some cases are impossible, e.g. an Aberration/Abomination with a vision would one-shot your droid before it can get close enough.

If the alpha has been tagged for several minutes, it can be worth to tag it again. Also, if you see an untagged alpha around your droid or pushing into your teammates, send the droid to tag it. For example, your droid left in power can encounter an Underseer which came to cheese. While it can be too late to stop the cheese, there can be enough time to find and tag it for the future.

#### When to defend and when to flee

So zombie is pushing towards or trying to cheese your mining. Do you invest into turrets and try to stop them, or do you just salvage the accelerant drones and relocate to a safer location?

First, you'd likely to loose some gas either way due to delays in mining. Evacuation would loose more mining time (since the droid has to relocate), while the defense would delay economic-related upgrades due to spending on turrets.

In early-mid game it's best to have several marines helping to defend, so you can get the economy snowballing. That's one of the easy scenarios. If there's a greater nydus burrowing towards you and there's almost nobody to defend, that's another easy scenario - just evacuate.

A tricky part is when marines around aren't enough to defend without you. In this case, a defense is probably the right call, as it prevents or delays a zombie from getting strategic rooms around. Diverts and an economy would be delayed, but that's fine. Turret kills would give some gas to compensate.

#### Defending early pushes and cheeses

First, get a sense of what's coming. Exploration droids would help to see a horde push and if there's an alpha coming too (ideally it would be tagged). If it's just a horde, get regular and/or flame turrets. If there's an alpha, get heavy turrets. Ideally you want both, but there may not be enough gas. Remember to arc turrets to boost their attack speed and to repair. Once the turret reaches around half of its hp, salvage it and place another once a bit behind. A nice thing about an arc is that you get a 100% cost refund and a turret charge back. If there's an alpha attacking the turret, start salvaging as it's about to hit for the first time, as it can take only 2-3 hits to kill the turret.

Cheeses can be usually predicted by a creep tower nearby. Zombie can place some sunkens and/or burrow alphas. Creep towers have a big range, so for example the one from the Overmind room in Subterranean can reach the rooms at science labs. Predict where the creep tower would spew and place some heavy turrets around. 2-3 turrets are enough to stop both sunkens and alphas. Move some of your exploration droids to the potential cheese locations, so that you don't have to constantly be around there.

If there's an untracked/unchecked Underseer, place some turrets in the gas mining to defend versus drop pods. Underseer can also let an alpha to deep burrow, so place some heavy turrets in strategic locations nearby (e.g. Containment, Power).

#### Hangar defense

When there are about 3 minutes left before fueling (2 actual minutes assuming diverts), start salvaging your turrets and accelerant/healing drones. It can take more time than you think. I'd recommend leaving psi disrupters unless you are starved on gas.

You want to be at the hangar once it opens. First, a zombie can give you little time to prepare, e.g. there can be an Abomination and/or a horde already waiting at the door. Second, it's way easier to get cut off once the hangars open due to a horde moving in, nydus spawning, or drop pods making the movement harder. You may have to seek another hangar and have a non-trivial chance of dying, wasting a bunch of gas you worked hard to collect.

Once inside the hangar, start with turrets and nukes. They'd be most helpful against the zombie push. Usually go for 6 heavy turrets or a mix of heavy and flame turrets if a zombie has mass lings. Next, get a psi disrupter and healing drones. If you have extra cash, put some sensor towers as a buffer. Be careful with path blocking, since sensor towers and turret hitboxes have weird interactions. Don't forget to upgrade the psi disrupter once it finishes charging.

Having more item charges is crucial here. First, it helps with a faster setup, as a trip to a locker to refill charges takes a non-trivial amount of time. Second, you have an easier time rebuilding and can set off up to 5 nukes total instead of 4, even if a zombie makes lockers inaccessible.

If you have enough gas, buy a tier 3 arc welder upgrade for a faster repair/charge or an attack speed. Also, put some gas canisters on the floor for the teammates, who'd often be able to get extra turrets, healing drones, nukes etc.

Keep charging, repairing and re-constructing turrets and modules during the push. If any damage is done to the hangar control, focus on repairing it. Don't abandon the post until a few seconds before the ship/train departure.

#### Accelerant drone positioning

When you get started with this build, just play around with the drone placement to get a feel for their range, buff through the walls etc. Don't worry too much about a perfect positioning and just get an extra drone if you have to. 3-4 drones would be enough to cover any mining.

There are optimized positions for multiple locations, which allow to use 1 less drone and still get 90-95% of coverage:

* Subterranean Science Labs: place 1 drone in the middle between the refinery and the elevator, and 1 in the middle of the sub level.
* Subterranean Omicron: place 1 drone to the left of the left refinery door so it hugs the wall (this way it would buff across the wall too), place another 1 at the top left of the U-turn near the hangar entrance and 1 more just to the left of the rocks "gate" near the mine.
* Subterranean Epsilon: place 1 drone near the south refinery door, another 1 slightly at the bottom left of the crossing and 1 more near the mine.
* Arctic Science Labs: place 1 drone in the middle of the sublevel and 1 more slightly to the left and below the north peak of the structure in the middle of the room (so it covers both paths above and below the structure).
* Arctic Alpha: place 1 drone at the bridge near the edge of the color change, another 1 in the crevice to the right of the starport and 1 more into the 135-degree corner above the refinery room.

#### To arc or not to arc

Tl;dr don't do an economy-focused arc build if you are one of a handful of higher ranked players in a team. You may do a good job at diverts, but a zombie can capture too much territory and/or disrupt your mining more easily. It's better to pick a hands-on approach and stop a zombie with a bare super stim shotgun or other weapon.

### Conclusion

This build focuses on an economy more and usually won't get many kills if zombie doesn't push your hangar. However, it would make your hangar very hard for zombie to take.

There's an alternative approach to playing arc, which doesn't do diverts and instead being active with turrets on the map. It's not covered by this guide.