Heavy Skills in Phoenix Point are active and passive abilities that the Heavy Unit can acquire by leveling up. There are 7 basic Heavy Skills and ??? Random Skills. Skills are restricted by unit level and Skills Points are required to unlock them. At level 4 Heavy Units will be able to select a second class unlocking that class weapon proficiency and all Basic Skills.
Heavy Skills in Phoenix Point
Heavy Basic Skills
There are 7 Heavy Basic Skills, and they are restricted by level. When a Heavy unit levels up it will be able to unlock a new Basic Skill by spending Skill Points. Below you can find a list of all Heavy Basic Skills in Phoenix Point.
Lvl 1

Heavy Training
Proficiency with Heavy Weapons, Mounted Weapons, and Jet Pack. (Jetpack requires 2 willpower to use)
Lvl 2

Brawler
Bash and Melee attacks deal 50% more damage.
Lvl 3

War Cry
All enemies within 10 tiles have their Action Points Reduced to 2 for the next turn.
Lvl 4

New Class
Choose a secondary class to train in.
Lvl 5

Boom Blast
The Action Point cost of Grenades, and other explosive weapons, is reduced by 1 and their range is increased by 50% until the end of the turn. (requires 5 willpower to use)
Lvl 6

Inspire
Killing an enemy grants allies 1 additional will point.
Lvl 7

Rage Burst
Shoot with a proficient direct-fire projectile weapon, using all remaining ammo in the weapon's magazine. (requires 5 willpower to use)
Random Skills
Random Skills in Phoenix Point are abilities that are shared among all units. Each unit have 3 Random Skills assigned from the pool. These skills are randomly assigned to any level from 1 to 7 and units will still need to spend Skill Points to unlock them. Below you will find all Random Skills in Phoenix Point.

PDW Proficiency
Proficiency with PDWs at +10% Accuracy

Shotgun Proficiency
Proficiency with Shotgun at +10%Accuracy

Heavy Weapon Proficiency
Proficiency with Heavy Weapons at +10% Accuracy

Steal Specialist
Additional +25 to steal of armor

Expert Heavy Weapons
Additional +20% Damage when using Heavy weapons

Grenade Proficiency
Proficiency with Grenades at +10% range

Handgun Proficiency
Proficiency with Handguns at +10% Accuracy

Sniper Rifle Proficiency
Proficiency with Sniper Riffles at +10% Accuracy

Expert Runner
Additional +2 Speed

Assault Rifle Proficiency
Proficiency with assault Rifles at +10% Accuracy

Expert Mounted Weapons
Additional +20% range when using Mounted weapons.

Expert Shooter
Shoot with +20 Accuracy

Devoted
Additional +2 to Willpower

Quarterback
50% bonus Grenade range and +2 Speed

Biochemist
All attacks that damage a target also inflict 1 viral damage (per bullet)

Cautious
20% bonus accuracy and -10 damage dealt

Farsighted
Additional +2 to Willpower and 10 Perception range

Reckless
30% bonus damage dealt and -20% accuracy

Expert Packer
Carry +25% maximum weight

Expert Thrower
Throw at +50% distance
So, strongman on a heavy, what does it do? Does double proficiency increase acc?
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