[Nidus Prime] is by far my favorite frame, some could argue he is the best.
for the love of god if you cannot understand how [Nidus] works this will probably be a hard build to understand, check the bottom of the guide if you don't understand the reasons for some mods

once his 2nd ability gets fixed so it works 100% of the time ill remove [Larva Burst] and replace it with [Augur Secrets] or [Augur Reach]

IMO late game build, wouldn't suggest for anyone who doesnt have the time a few endo steel path grind sessions

the arcanes are a pain to get, completely up to you if you have them or not but [Nidus] becomes a brick with [Guardian]

if you cant afford an umbra forma just keep the exilus mod slot empty until you can as you only usually have a drift mod in there anyways, example
once you do get an umbra forma just move the zenurik forma to the exilus as most of the good ex mods are zenurik polarity, but if you want to have some room you can always remove the zenurik polarity as some good ex mods dont have the zenurik polarity

[Larva Burst] is because his 2 is horribly buggy, a majority of the time it wont grab enemies on high level survival, disruption or defense so its there to recast, the damage is useless
[Adaptation] is unranked because you dont need to waste 5 capacity slots for another 5% damage reduction it seems pointless outside of boss fights and thats extremely situational

[Flow] and [Primed Flow] aren't needed as [Hunter Adrenaline] makes him have infinite energy, i've never had a problem with running out of energy
[Sure Footed] isnt needed either, his 3rd ability when used stops knockdowns

also [Abundant Mutation] isn't used as 30 seconds is way too long for undying for another 100 stacks, the mod imo is just a useless weight as ive never seem to need more than 100 stack