DOOM

These three achievements are a set of grind related as you need to reach certain Echelon ranks. To summarise, here are the needed Echelons:

1. Unto the Evil (Robotic Armor):
   Computing with Style - You need to reach Echelon VII, but the earliest is reaching Echelon V.

• Scalper - Headshot Kills (Unlocked at Echelon V)
• For the Glory - Glory Kills across all modes (Unlocked at Echelon V)
• Power Outage - Shutdown Medals (Unlocked at Echelon VI)
• Stain the Streak - Show Stopper Medals (Unlocked at Echelon VI)

2. Bloodfall (Evil Cultist Armor):
   Fashion Fanatic - You need to reach Echelon IV, but the earliest is reaching Echelon 0 Level 2.

• Reaper Mastery (20 Reaper Kills)
• Blood Brother (Assistant Commendations)
• Olympiad (Marathon Runner Commendation)
• Hellshot Mastery (20 Hellshot Kills)

3. Hell Followed (Cyber-Demonic Armor):
   Beauty is Pain - You need to reach Echelon X, but the earliest is reaching Echelon VIII.

• MVP? More Like LVP - Kill the top enemy three times in a match (Unlocked at Echelon VIII)

Luckily, there is a way to earn EXP and the max cap per Echelon rank is after Lv. 50, you need to play on a Sector map just by capturing points from point A to B then B to A the same goes to your team and the opposing team, it is a matter of grinding exp and persevering through. Here is a video down below for an example it is pretty straightforward. The grand total to hit Echelon VIII is 1982000 EXP.

Credits (All from PSNProfiles Guide):
Robotic Armor
Evil Cultist Armor
Cyber-Demonic Armor