If you're a F2P, you won't be able to get the ninjas within the time period. Also, you can get Kisame from the exchange shop, farm Yamato from elite instances.

That leaves you with Orchimaru which you need 1600 points to fully redeem him, which is impossible for you to get that much points unless you spend ingots.

Your best bet is either magamatas or mood scroll since stamina potion can be obtained easily. Get magamatas if you haven't hit level 3 magamatas since they provide a standard power boost.

Alright thanks :)

u get Yamato for free from lvl 70 Elite instance.

As F2P I think mood scrolls are actually better than the magatama this go around, minus some exceptions. The only reason I say this is because you can get 20 scrolls from the shop in this event. As F2P, ONLY USE THESE ON YOUR MAIN RIGHT NOW. I can't stress that enough. Most of the ninjas you have at the moment aren't going to be with you in the long haul but your main always will. At the bare minimum you would get your main to level 7 mood which is roughly +30%/-5%, which comes out to a few hundred BP as you progress in level. The only real exception I can think of would be if you are in a very new server and you desperately need the magatama but, even then, I think the scrolls are likely better in the long run since there are so many opportunities for magatama.