Hi guys !
For this achievement you must have all 19 weapons in your inventory in the same playthrough.Most of them are story releated but 3 of them are missable.All 3 are in secret areas.
Those 3 are:
- The Bastard in level 1 (Landing Pad)
- Bloodaxe in level 3 (The Hive)
- The Knife in level 5 (The Tomb)
You can check this video to find them all (credits to MetroidvaniaX)
Or you can use this guide if you only want text and pictures (credits to Taake)
Happy hunting and enjoy Valfaris !