Class Guide ~ Engineer

High HP & Stable Damage

Gun Training: 20 (Each Lv, P-ATK and M-ATK +1% when equipped with gun)
Smelter: 15 (Each Lv, Max HP +1%)

Critical damage build

Gun Training: 15 (Each Lv, P-ATK and M-ATK +1% when equipped with gun)
Wave Mechanics: 15 (EachLv, Cri Rare and M-Crit Rate +1%)
Electromagnetism: 10 (Each Lv, Crit DMG and M-Crit DMG +2%)

Defensive Mecha build

Forging Knowledge: 15 (Each Lv. Physical Damage resistances +1%)
Smelter: 15 (Each Lv, Max HP +1%)
Alloy Knowledge: 10 (Each Lv, DEF+1%)

Versatile build

Smelter: 10 (Each Lv, Max HP +1%)
Gun Training: 10 (Each Lv, P-ATK and M-ATK +1% when equipped with gun)
Forging Knowledge: 10 (Each Lv, Physical Damage resistances+1%)
Alloy Knowledge: 3 (Each Lv, DEF +1%)
Improved Output System: 5 (Each Lv, STR +2%. Requires 25 knowledge points)
Condensed Oil: 1 (Each Lv, Oil Bomb.P-ATK damage per second & Skill DMG +10%. Requires 35 knowledge points, Improved Output System 5 points)
Energetics: 5 (Each Lv, MP Requirement for skills -2%. Requires 30 knowledge points)
Material Research: 5 (Each Lv. Healing effect of Armor Repair +3%. Requires 35 knowledge points, Energetics 5 points)
Improved Motor: 1 (Each Lv, Missile Destruction, summon LV5 Mini Robot. Requires 35 knowledge points)

~ I hope it will be useful!