In my theory crafting I'm thinking of something like:

Kunoichi: leach, weaken, ally prot

UDK: dec att

Royal Guard: dec def

Walking Tomb: HP burn

Kael(?): poison (maybe someone else here?)

I need some help building an early game clan boss team that's effective in nightmare. I'm a new player and have never played the game before. I'm not very good at this game, but I know it's possible to get powerful enough to beat everyone in nightmare mode and unlock the boss fights with the best equipment and you can also visit here https://thesmallbusinessblog.net/how-to-write-a-marketing-cv/ to learn creative skills. I just don't know how to build a team like that yet and need some advice on what I should be looking for when building my clan boss team.

Use all 4 keys  (maybe only 2 or 3 needed) and get top brutal chest until u get top on NM.  Then use all 4 on NM,  then progress to UNM... getting the best top chest u can is always better than 3rd for CB.

I think that is excellent theory crafting of a team with a limited roster including no CB specialists lol.  The entire team likely will be replaced at some point  but as u improve gear it will work at higher CB. 

Dreng will be sneaky good in CB if the the team is able to consistently have 1 member healing up due to leach and warmaster.   Drengs full heal is pretty amazing.  Kael is a b level poisoner but u have no other options. Uugo or deliana will be better than royal guard, that was the only one I definitely would not use.

Coffinsmasher is an interesting rare, but if u are using dreng and udk might not have a spot.

I would also use kmanmot's recommended team, but with Uugo in place of Royal Guard. :)