Allow the player to get "expert melee weapon user" for their respective melee weapon category of choice, allowing to boost their respective melee weapon with fitting bonuses and unlocking specific active abilities.
(As far as I know, Sledgehammers already start with Pummel in Infusion)
Feat: "Expert Sledgehammer User"
Requires level 10, 9 Strength and 60 base melee skill
+20% base damage for Sledgehammer attacks
+15% critical damage for Sledgehammer attacks
+20% stun chance for Sledgehammer attacks on biological targets
+25% base damage against automatons for Sledgehammer attacks
Unlocks Super Slam and (possible new 4th Active Sledgehammer Ability)
Feat: "Expert Spear User"
Requires level 10, 8 Strength and 6 Dexterity, and 60 base melee skill
+1 melee range for Spear attacks
+20% armor piercing damage on biological targets for Spear attacks
+2 range, +10% base damage and +10% Chance-to-Hit for Spear Throw
Unlocks Spear Throw, Impale and Sweep
Feat: "Expert Knife User"
Requires level 10, 9 Dexterity, 60 base melee skill
+10% crit chance for Knife attacks
Critical attacks ignore 25% of the enemy armor on biological targets for Knife attacks
Guaranteed critical strike when attacking a biological enemy from behind during stealth for Knife attacks
+5% base damage when attacking a biological target from behind
Unlocks Crippling Strike, Cut-Throat, and Eviscerate
Feat: "Expert Sword User"
Requires level 10, 8 Dexterity and 6 Strength, 60 base melee skill
+10% chance-to-hit for Sword attacks
+1% crit-chance per Sword hit on the same target
+20% Riposte damage
Decapitate ignores 25% of a biological target's armor
Unlocks Flurry, Decapitation, Parry and Riposte
Feat: "Expert Fist Weapon User"
Requires level 10, 7 Dexterity and 7 Strength, 60 base melee skill
-2 Action Point cost for Fist weapons
+10% chance to incapacitate biological enemies for pneumatic Fist weapons, +10% base damage for pneumatic Fist weapons
+20% electroshock AoE and damage for electroshock Fist weapons, electroshock Fist Weapons have a 5% chance to stun automatons
-10% energy usage on Fist weapons
Unlocks Heavy Punch, Dirty Kick and (possible new 4th Active Fist Weapon Ability)
