Oppai has a Skill trial google doc.

https://docs.google.com/do*ent/d/1NugtF12K5S1lPNH1vkE2cp5mjV9kEvJDLdaWFY_V610/edit its going to censor the "come" in do*ent so you gotta replace that.

As for ninjas that dont cost to skillbreak that are used in CN? Idk, i dont really follow CN lineups as i play NA. But definitely skillbreak Kurenai and Lee. Pain Ningendo and Gakido look to be pretty good with skillbreaks/trial (as far as ones you can get frags for without spending coupons)

If you want to know ninjas from elite instances that are "lee and kurenai type of good", then they would be gaara 5th kazekage and sai. The rest of the ninjas in elite instance that have skill books/trials are not worth the time.

Treasure rares that can be farmable in ninja scrolls and treasures such as pain ningendo, gakido, chojuro, shikamaru (chunnin), kakashi beheading, ay 3rd (I cannot remember if he's farmable in ninja scrolls), danzo, fu, and maybe mifune?

To sum it up, excluding ay 3rd since I can't log into my china account to see if he's farmable in ninja scrolls, you can only farm good support/secondary damage ninjas.

Already sbed/5 starred kurenai a while ago and finished lee a few days ago. I haven't unlocked ningendo's instance, and my server is too dead to do GNW to get credits for gakido. Any other way I can get group credits besides GNW?

20 Activity Points gives 300 group shop points

SA gives group victories

Idk but i don't see how sai's skillbreaks are good. Suigetsu's dodge breakthrough seems good, and shino's y skills look interesting too. Asuma wb's y passive might be good as well.

I added sai for the reason why people believe sai suit is op in arena since he basically becomes like him. His mystery-Y, 2nd and 3rd passives is nice to have if you don't have enough ninjas to build better teams. If I wanted to compare "goodness" in a ninja's skillbooks/trials, sais would be below kurenai/lee/kazegaara for sure for the ones that can be farmed in EI,

Dodge only works for a ninja if they can do a lot of damage and suigetsu doesn't. Shino is quite ok to use in arena as the bugs are meaty but outside arena, skillbooks/trials won't make a huge difference in usefulness. Of course, I can't judge how you think what seems good as you'll find out yourself once they come to this server.