Sycl of Drakes deserves all the books. Heal, Revive, max her out I say.

Scyl is very good without books, I am not saying she isn't better booked but they are not needed on her at all.

Definitely need more detail to answer the question though. Where are you looking to improve? Doomtower? Tag arena? Where are you at in each of these and what does the rest of your roster look like?  Unclear on FW, are all the others 3star, I am guessing not otherwise you would be saving books for Lydia. 

If you plan to use Rhazin in cb in the future then try to max at least his A2.. Max A1 is also good for additional damage. 

Scyl is good in almost all content so maxing her skills is good. 

Kymar, I don't see any need to max his skills. I use him in some of my speed runs but most of the time he just need to use his reset cooldown once. So I think upgrading his skills is not a priority. 

Ghostborn, there are already a lot of decrease defense in the game that I don't have a use for him. He is just sitting in my vault. 

Iron Brago, I am using him in gold4 3v3 without books and he is just working fine. Of course, if you plan to use him in cb and also want to maximize his damage in arena/3v3 then you may want to max his skills. But with the amount of books required, you may want to weigh your priority first. 

You didn't tell us what your Clan Boss team was.

Rhazin might be a good fit in your Clan Boss team which would require him to get books on his A2.

Agree  with  Trips,  no  need  to  book  Scyl.  I'd  try  a  few  on  Rhazin.

To Answer Trips and Player J

Clan Boss: I have an unkillable team that is comprosied of Maneater, Painkeeper, Kreela, OB. The final position switches out based on affinity (Bulwark, Frozen Banshee and Cagebreaker). I am able to 2 key NM and 3 Key UNM. I am now in the process of switching my team to now be based on affinty. The team will be Maneater, Painkeeper, Kreela, Frozen Banshee and Gravechill Killer (GK being the stun target). I'm hoping that everyone with full gear and masteries will 2 key both bosses. If not, I will create a new UNM team with ME, PK, FB, Septimus and OB as the stun target.

FW: Let me explain better. I've 3 starred all of High Elves and I have 60 stars on Orc, Dark Elves and Demonspawn crpyts. Half the others are low 50s and the rest are 30s. My goal for using the books was to maybe help carry through FWs, but would it be worth to get through that final stage?

Doom tower and FW is what I am currently working on. With all the changes they made this round on the bosses I found myself not wanting to push pass floor 30 hard. 

Right now I am filling out my roster so that I can complete as much of faction wars as possible. I am going about it the wrong way and leveling various characters to level 50 rather than doing what I usually do, which is build, level and master one character at a time. 

So, back to the point, Scyl, Tyrant and possibly Prince Kymar are used most outside of the FW. I only need to be the boss to complete DS FW whereas Barbanian faciton needs help. Rhazin would be a good choice too since that faction is in the mid 30s, but I think I need leveled champs rather than just books.

As always, thank you, I appreciate the insight.

You seem to be in a similar sitution as to me.

I am doing Faction Wars as well.

I think your going to need to save your books for Faction War heroes 100%.

I can speak from experience.

A few days ago, I ran out of Epic Tomes completely.

What are some of the Teams you are running?

i would not use lego books for fw progress at all, unless u are down to last few factions. i can expound further if necessary, but it should be clear that finishing any particular faction does not warrant it. you are likely on expediting an eventuallity, patience is key...

you are only at 30 doom. your focus should be there and getting gold tag arena.  I am at 114 of dt, so i am hopefully a week or 2 from gold tag.  

the best choice may be to not use books on any of those. i dont have pk, that cd reset may be more useful than u think as high level doom floors are long battles

I have 47 epic books that I am about ready to spend for the same purpose. I am hoping to partially book a few of them and get lucky with my RNG. I am saving 15 books for Archmage when I finally get him this month.

High Elves are done, so no note there.

Dark Elves (60 stars) - Ghostborn, Kael, Painkeeper, Kaiden and Madam S. I have coldheart as well, but even with a DEF chest, she dies pretty quickly. I have Psylar leveled to 50 with no books and partially ascended. She'd probably switch in for painkeeper or kael, but not sure if it will be enough. I have Visix, but I don't want to 60 her JUST for FW. Seems like a waste, but could be necessary.

Orcs (60 stars) - Kreela, Iron B, Sandslashed, Zargala (all ascended and gear) and then Vrask at level 40. Getting Vrask to 60 might get me to beating the stage, but I don't think it will cut it. Shaman has revive, but I am hesitant to 5 star her.

Demonspawn (60 stars) - Duchess, Tyrant, Drexthar, Alure and Umbral/Peylar/Prince Kymar. I feel like some combo will get me to 3 star the boss.

Dwarves - Melga, Rockbreaker, Grizzled Jarl, Bulwark and Kurzad. I just pulled Fodbar and Gala and I think they will replace Bulwark and Kurzad.

Barbs - Scyl, Turvold, HK and Skytouched. Honestly, this team is a mess and needs revamping. I tried Marked, but WM will probalby be a better fit.

Sacred Order - Cardinal, Armiger and Ash. Just pulled Fenax, but i don't really have anyone else to fill out the team.

Banner Lords - Septimus, Oathbound, Seneschal, and Dagger. Archmage will fill out this team. 

Skinwalkers - Basher, Warchief, Smashlord, Ursine Ironhide, and Fleshmonger. This group also needs a lot of fine tuning.

OG - Shatterbones, Man Eater, Ghrush, Bellower and OB. I just pulled Galkut, so he will take OBs place. 

Lizardmen - Rhazin, Bloodbraw, Jarang, Jareg, and Haruspex. Except Rhazin, all are under development. Nothing else worth mentioning.

Undead - Dark Elhain, Zelotah and that's really about it.

Most of the epics I listed are level 50, unbooked, no masteries and only partically ascended.  I have a LOT of work to do....

I got to floor 60 last time, but did not feel like getting through the scarab boss. The changes they  made to turn meter reduction kind of screwed me over. My scarab boss team was lyssandra, MM, Coldheart, Armiger (in destroy gear) and Alure. I have MM going first with divine speed boots so that he is always getting his shield off. Even doing it manually once or twice, I didn't get pass level 30. A few more attempts may just do it this time around.

I'm not really convinced tag team arena is worth the time and investment. Its just so much time and balancing for not that great of rewards.