What worked best for me in case of collecting nameless venom is: using a spinosaur wich is levled in health.

Wait until a few nameless are attacing you - give them one attack with the spino (2leg attack lode on) run behind them, see if enough are spawning new. You can turn pretty well in spinos two leg attack mode to see if there are still enough namelesd to respawn. Don't kill them all at once, it takes more time to spawn if all are dead. You can kill anyone around you only if you see the dirt cloud of anew one spawning in front of you.

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