You have 7 days to collect keys.I'm sure that there will be key pack in some of the events.You can do SA and TI for moon scrolls,as well as arena missions and ninja test.Also,if you can kill fast enough rogue ninjas,you can make 20-50 keys,depend of competition.

every month cave key rebates usually bro... u shud save upto 2k keys to garuntee get the ultimate escence ..recommend u to save it since cave keys can be easy obtained from great plates and other events.. plus its for 200 moon coins so yeah save save save till u die P

You meant to say 1050 keys for the ultimate essence jackpot. Saving 2100 keys will give 2 ultimate essence jackpots.

Hello!

In my opinion, it is better if you will save up your Cave Keys for now, if you aren't able to gather up 1050 until the last day of the Rebate. Doing it partially or in small amounts isn't beneficial and you will lose the potential of gaining more items from the rebate. It's okay to skip a rebate if you're not rushing your Cave Key Runes but if you are, then you better collect Moon Scrolls from different Daily Missions and Events or redeem Cave Key Packs from events. At most, 1050 would be fine but if you can collect 2100 then it is better.