I had installed 2 Azure Archon Shard for 50 energy each, 100 in total.
If you are lacking energy, try replace the [Augur Message] for a [Flow].
2 Crimson Archon Shard for 10% duration each, 20% in total.
You can replace [Augur Secrets] with [Augur Message] instead.
1 Amber Archon Shard for effectiveness on Energy Orbs.
Just in case run out of energy, you can replace with any other stuff you like.

Just remember always had skill 3 running to help you survive.
I had replaced skill 4 with [Xata]'s Whisper for damage, and it work really great using [Felarx].
Especially peace maker is useless since it won't shoot boss.
Also remember to keep skill 2 running for more damage.
Skill 1 is really useful when you are going to one shot with shotgun, especially you only had to use it once and use it again to release it whenever you want.

Felarx build:
https://overframe.gg/build/382649/

Videos:
https://www.youtube.com/watch?v=QFYGw0bDDEI