Remnant: From the Ashes
50 Achievements
1,500
64-80h
Not So Special
Defeat 100 special enemies
50
19.24%
How to unlock the Not So Special achievement in Remnant: From the Ashes - Definitive Guide
Now all these can be farmed at any time you want. Find a spot you are comfortable with on the map and go explore an area that usually spawns one every time. Simply kill it and head back to the checkpoint crystal to rest. It will re-spawn all the enemies and the specials ones as well.
It also comes to my attention that the special enemies also tend to drop lumenite crystals. So pay attention for that as well.
For the enemies that I came across so far are:
Guy with duel blades
A big guy with a long sword who runs at you
A screamer who spawns enemies
An archer
A mini-gun guy
The regular root who burst into flames
Now I know there are a ton more, if anyone wants to add them in the comments be my guest.
You will encounter special enemies as you make your way through the worlds and they are stronger and do more damage than basic enemies. You will know when you are fighting them, not only from their obvious difficulty in defeating them, but you will be given an audible cue both when they spawn and are defeated. You will very quickly accustomise yourself to this sound as it is very distinct and serves to warn you that you'e in combat with a special enemy.
The special enemies come in many different forms, however you will fight and kill these throughout your minimum two playthroughs, so defeating 100 will almost certainly come without actively trying to find them.