Spear is a new DLC melee weapon class, which has several interesting features and an entirely new mechanic(Spear Throw). Played with the first build(at the end of the guide) all Expansion content on the highest difficulty.
Strong Points:
Spear Throw - very high ranged attack which inherits almost all melee bonuses, so you could incapacitate the enemy with the lucky spear throw.
Good armor-piercing
Best blocking system - can be easily buffed up 100% chances.
reliable AOE attack (Spear Sweep) - Try using this attack with Electroshock Generator
All spear feats are pretty nice
Weak Points:
Low damage per action point values compared to other melee weapons
need DEX and STR investment
no melee action point reduction from high DEX
high mobility is a must - you need to throw and retrieve your spears all the time
Unique Spears variety and quality are pretty bad
There are two main paths to build your spear guy - going either STR(classic) or DEX. Each way have their cons and pros.
STR: more damage, carry capacity.
DEX: more crit chance, initiative, skills bonuses(at least Throwing and Lockpicking).
I will use the classic version of Spear build with the addition of high AGI and new Psi school - Temporal Manipulation for more mobility, action points, and utility.
Starting stats: 10/5/10/3/3/3/6. +1 DEX on lvl 8, and +1 AGI on lvl 24, put all other stats points into STR.
Skills:
*Melee: MAX
*Throwing: MAX, used for Spear Throwing, Nets and grenades precision.
*Evasion: MAX, but can be sacrificed for some urgent needs. The primary defense against AOE attacks and ranged enemies. Will be modified by Nimble(+15%), Jumping Bean(+25%) and Adrenaline Shot(30%).
*Stealth: 50-60 is enough for comfort play. Keep in mind that effective value will be much higher due to the high AGI and all items with stealth bonuses(including Cloaking Device).
*Hacking: 84 is more than enough(in case DC checks will become higher). You want to have 100 effective hacking for some content in the Black Sea. This value will be further modified by INT, Huxkey(+15), new DLC armor(+10), Electronics synergy, Underpie(+3) and new INT medicine(+2 INT).
*Lockpicking: 80 is more than enough(in case DC checks will become higher). This value will be further modified by INT, Jackknife(+7), Huxkey(+15), new DLC armor(+10), Mechanics synergy, Underpie(+3) or DEX food(+1-2 DEX).
*Mechanics: 90-100. 90 is you want to craft spear with house bonus(+15%) and +2 INT item and don't want to rely on random metal plates from the DC. 164Q is max metal plate quality you can find before DC. So there is no reason to go higher than 131 effective mechanics. I bought 155Q metal plate in Foundry, so I could comfortably craft my spear without INT medicine.
*Electronics: 110-120. 105 effective electronics for EMP Grenade Mk III, 135 - Plasma Grenade Mk III, as high as you want for Shield Emmiter(for top energy shield Emitter with best secondary modulator, but can be easily tuned with your skill), ~150 - for best Energy Edge Emitter or Electroshock Generator for your spear(before DC).
*Biology: 63/95. 63 For crafting all important medicines before DC with all possible bonuses(house, +2 INT medicine and Underpie). 95 if you want to go into Supersoldier Drug crafting in DC.
You will use Jumping Bean, Adrenaline and Focus Stim all the time, so 50 effective skill is the must.
*Tailoring: ~100. I advise investing in tailoring up to 50 effective skill for advanced repair kits crafting and then stop before you will have some spare skill points, good leathers, overcoats, and Super Steel Plates. High lvl leather armor crafting is very expensive, keep in mind. You could buy some high lvl(up to 2310/2310) tabi boots in top shops and loot good enough armors or use Rathound Regalia which is even better choice. Investing in tailoring is luxury.
For the Infused one's armors look into Cave Hopper(extra AGI, movement points and speed), Rathound(extra crit chance) or Siphoner/Greater Siphoner(extra evasion/dodge). For the tabi use either ninja(+stealth, pretty easy to find and craft), Cave Hopper(-Sprint cooldown, extra AGI) or Siphoner(+dodge/evasion and slow immunity).
*Temporal Manipulation: 55/70. You need 25 for Limited Temporal Increment(cooldown reduction), 55 for "Haste" psi ability, 70 for Stasis which isn't must, but good to have. I advise you to not to take the Psi Empathy ability at first and invest in this school after some time. Spear build is pretty comfort to play in the beginning areas thanks to the blocking and spear throw even without it.
*Mercantile: 80. Main reason - special merchandise from shops and some money management(in higher difficulties you will have some troubles with money, because of recent selling rates changes). 105 is max which needed for Efreitor Hanna's shop, 100 - for Expansion shop with Supersoldier Drug. 95 - for another Expansion shop with medicine components. Can be buffed by Undepire(+3) and +2 INT medicine.
*Persuasion(optional): you could invest some points into Persuasion. You want to have 80 effective value for all important Black Sea values. Can be modified by Tchortist Noble Robe (+1 Will) or Heartbreaker Serpent armor(+10), Heartbreaker Serpent tabi boots(+10), Mercantile Synergy.
*Chemistry(optional): 112 effective chemistry is required for crafting Frag Grenades Mk V. Completely optional cuz now we have Plasma Grenades which are related to Electronics. God to have if you will go into critical grenades route.
Crafting skills are usually tuned by the components you could find. So if you don't have top lvl components there is no reason to invest in the corresponding skill heavily(Electronics is an exception) and better to lvl up something else. First of all, you want to craft a good spear. You can skip electro modification(you won't have much money to keep it in shape), then lvl up biology(up to 50 effective after completing Depot A), and lvl up mechanics, electronics, tailoring for 50 effective skill, so you could transform items into repair kits.
Feats:
Important Feats: Sprint, Spear Throw, Fend, Impale, Cheap Shots, Spear Guardian, Expose Weakness, Critical Power, Sweep, Psycho-Temporal Acceleration
Optional but nice to have: Blitz, Nimble, Weaponsmith, Recklessness, Opportunist, Grenadier, Paranoia
Important Veteran Feats: Increased Agility -> Expert Sprint(13 AGi requirement)
With infused hopper tabis Sprint will have 5 turns cooldown(can be lowered by using Limited Temporal Increment further), which lasts 2 turns. Going into 13 AGI is completely optional, you could skip this route and instead pick 7 DEX with Grenadier+Three-Pointer which will be even better(Plasma grenades have very high damage values on crit), If It fits your playstyle.
Avoid taking Iron Grip feat. You will just get -15% damage with shield, limited mobility with no real use. Junk feat.
Specializations:
Important specializations: Spear Guardian, Spear Throw: Action Point Cost, Cheap Shots: Critical Damage or Critical Power.
Few words about specializations:
Spear Guardian - 100% blocking chances with the spear. So you could easily tank most melee enemies without any % lottery. High lvl spears will have ~40 blocking damage values and with Fend It's 100(yay!). Just do not try to block sledgehammer attacks...
Spear Throw: Action Point Cost - Spear Throw AP cost 25 -> 10. And you could throw 2 deadly spears with Limited Temporal Increment only for 25 AP(10+10+5). Spear Throw is very deadly, on crit it could even kill some boss in 1-throw.
Cheap Shots: Critical Damage or Critical Power - more crit damage.
Overall:
Picking the spear(new Rearm ability, just move it into the action bar, you will use it a lot; Alternatively, a spear can be picked out of combat just by moving onto it) after throwing cost no AP, so you want to have high mobility for running and picking your spears in the combat. You need to use goggles with night vision to throw your spear in the darkness with good to hit chances. Spear throwing damage is modified by the distance, so if you could throw a spear with 8 tile distance and good hit chances, do it. Spear Blocking is helping a lot at the beginning of the game and even more in the Depot A section (blocking Mutant heavy punches).
Also, keep in mind - to achieve blocking "stance" you need to either land successfully hit or to use Fend ability. Without it, you can't block. The spear can be even recovered from the water. Best belt to use is Doctor's Pouch(medicine consumption 10 AP -> 2 AP). Your main equipment: Motion Tracking Night Vision Goggles, leather armor/tactical vest, tabi boots, 2 spears, low+low or low+mid Shield Emitter, Doctor's Pouch and utility items at your discretion.
http://underrail.info.tm/build/?Hg4GCwMDAwYAwqAAwqAAwqA9VFAAAGTCggBfZAAAAEYAAFAkOcKVwpLClBLCkwZLwqxHK8KHADHCscKlJuKdjQris44C4rOiA9-_ - Spear build #1 (classic build + 13 AGI + Temporal Manipulation + Supersoldier Drug crafting, without Persuasion)
http://underrail.info.tm/build/?HhAHCAMDAwYAwqAAwqAAwqA4VEwAAGTCggA8ZAAAAEYvAE0kOcKVwpLClBLCkwZLwqw-K8KHFgDCtjEm4p2NCuKzjgLis6ID378 - Spear build #2 (classic build + 7 DEX + Temporal Manipulation + Persuasion + Crit Grenades)
P.S. I will add some video later. It's pretty spoilerish xD