Introduction
Nb. This guide is probably equally applicable to Engies too, it also assumes a certain familiarity with concepts such as base stats and common abbreviations for skill names.
Symbiants are the Shadowlands version of implants but unlike Rubi Ka implants you don't need to add clusters they come prebuilt. Also unlike RK implants rather than adding to just 3 skills they add to many. The symbiant head for instance adds to all nano skills (bm,mm,pm,mc,ts,si,fa,treat) and many more.
Here's a comparison of the nano skills from a typical ql140 charm/calm RK implant setup and a ql 140ish full symbiant set.
Rubi Ka cluster based implants
mm 0 bm 73 pm 105 mc 30 ts 43 si 73
Shadowlands symbiants
mm 145 bm 143 pm 143 mc 160 ts 160 si 157
As you can see you can have your cake and eat it. This is also by no means the end of it - the set will also buff just about everything else you could need including base abilitites and psychology. Not only this it will buff them higher than even the most balanced RK set could come close to.
The only significant caveat to this is that apart from a small amount of pistol there are virtually no weapon buffs. But with the enormous boost to nano skills and basic stats maybe its time to go nuke/pet defence armour and stick to CDRs.
Symbiants drop exclusively from pocket bosses - more on that later.
Availability
There are two symbiant ranges available to crats Control and Extermination. Of these the Control set is so superior to the Extermination set that the Control set that its clearly the one to use if you can. The control set is obviously aimed at Crats and Trade skillers.
Having said this at this time the Control set is more difficult to come by than the Extermination set and the extermination set does most of the important things.
The jewel in the crown (as it were) of all the symbiants is the head, so here for comparison is what the Control head buffs as opposed to the extermination head.
Control Int,Psy,Sense,Psychology,max nano energy,nano pool,Nano init,Nano resist,bm,mm,pm,mc,ts,si, first aid,treatment,pharm,chem,qft,me,ee,ws,tutoring, comp lit,nano prog,perception,veh air,veh wat,veh ground, map nav
Extermination
Int,Psy,Sense,Psychology,nano pool,nano init,nano resist,bm,mm,pm,mc,ts,si,treatment,qft,comp lit,nano prog
Both sets are available in qls 1-300 in steps of about 10. Note, not all parts exist at all qls. For instance the Control ql100 set does not include a head but the 110 does.
Requirements
Unfortunately symbiants are not very easy on your base stats + treatment. Every single base stat is required somewhere - though you can focus on some more than others.
All symbiants have high treatment reqs for their level so don't expect to get them in too early.
The Control set requirements are
Agi,Int,Psy (head/ear/leg/waist)
Stam,Int,Psy (chest/left hand)
Sense,Int,Psy (eye/left arm/left wrist/feet)
Str,Int,Psy (right arm/right wrist/right hand)
The Extermination set requirements are
Agi,Int,Psy (feet/left arm/left wrist/right arm)
Stam,Int,Psy (head/chest/right hand)
Sense,Int,Psy (eye/right wrist/leg/waist)
Str,Int,Psy (ear/left hand)
Clearly Intelligence and Psychic are key regardless of what you plan to implant. Unfortunately to maximise nano skills, every single other skill is also required. The nano skill symbiants in order of importance are (head,eye,chest,ear,right hand,waist). So I would say the symbiant crat's primary base skills are therefore Agi/Int/Psy to get the best control head in or Stam/Int/Psy if you plan to use the Extermination head.