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This is awarded for clearing the Mr. Tomassi mission (beating Tomassi for a second time).

*Edit* I just saw that Mortifervs has added a separate solution that covers getting to the mission in the first place (thanks). So I'm adding here to improve the guide:
Here's how to beat the mission:

Mods
I left this achievement until last so I had the best mods available. I equipped three health boost mods (two level 4 and one level 5).

Weapon
I only used Pierce when attacking Tomassi, with rate of fire, reload speed and damage mods. Shatter is a good back up weapon for the other enemies.

Hiding spot
There's a great hiding spot under the walkway on the right hand side, in a little alcove. Tomassi can't hit you from here but you can hit him. From here, it becomes a lot easier to manage the other enemies, and you'll be able to gather health drops fairly easily. When the Hiss Distorted (invisible shrieking things) show up, make sure you kill them as soon as possible.

Bonus tip - bring a healer
In the Turntable room before you go into Sterling Awe, a Hiss Cluster sometimes spawns. If it does, knock its health down but don't kill it. Seize it and it'll be able to follow you into the boss fight and heal you as long as it stays alive.

I found this by far the hardest achievement. It's a horrible, frustrating fight and took me about 20 tries...good luck

Narcotic Radar just below have done incredible job, making everyone's life easier! The only thing I want to add, is info for the people like me, who are struggling to find the way to even start this mission.

How to get this mission?

1) Mission to defeat Mr. Tomassi (again), becomes available during Finnish Tango main story mission.
2) To get it, talk to Emily Pope in Board Room / Central Executive.
3) Get to Turntable / Containment.
4) Room with Mr. Tomassi is on your left, when you first enter Turntable.
5) Kill Mr. Tomassi.
6) To get achievement and skill points, talk to Emily Pope again.
7) ???
8) Profit!

Settings - activate one-hit (just tip in the box).
All enemies, including bosses, die with just 1 hit.
Do it and the achievement is yours 🤘
It took me 3 seconds to kill Mr. Tomassi

After you finish killing all of the enemies, head back to Pope in Executive floor to talk with her. That will finish the side quest and the achievement will pop.

Follow the other guides to find tomassi if you find it difficult to locate. The others guides didnt work for me.
I was frustrated rage quit and went to sleep. The morning it came to me.
The best weapon to use for is grip.
A suggestion is to max health, energy put some to shield and lauch.
During all the fight spam lauch to tomassi, he will avoid the first but cant avoid all. When he launches hide behind rocks.
Whe. The health bar is low and enemies spawn the invisible will spawn too. Press shield and hold it until the invisible hits you, the shield will take all the damage. Try to kill invisible asap. Shield and one lauch should take half your energy, always keep some to avoid with B button. After the invisible is gone kill the spawns. Dont bother with tomassi cause the things that blow come from all directions. No need to hide under stairs or anything just try launch launch launch...