To everyone saying that Nightmare is "2x the rewards of normal", this is completely not true, it is a lot more than that. From my run last night I estimate it to be about 4x normal for people that are not VIP, and double that (8x normal) for people who are high enough VIP. My last chest had 12 items for example (they were all crap but that is besides the point).
01: 148716 2x xp vial, 2x random
02: 156288 2x flora SS, 2x random
03: 169900 4x blue, 4x random [200 coins]
04: 300000 2x purple, 2x random
05: 307218 2x blue, 2x random
06: 311642 4x blue, 4x random [400 coins]
07: 469550 2xp xp salve, 2x random
08: 470238 4x random
09: 487112 2x m. dust, 6x random [600 coins]
10: 653042 2x blue, 2x random
11: 653128 4x random
12: 674340 2xblue, 6x random [600 coins]
13: 844382 2x blue, 2x random
14: 849308 2x flora SS, 2x random
15: 884396 2x purple, 10x blue [800 coins]
So I was wrong... but not as wrong as you...
I end up with the exact same amount of gold I would have gotten with 2 normal CoF runs. I end up with 2x the amount of CoF coins I would have normally gotten. (But we already came to that conclusion and that makes it just a very shitty double cof coins event)
Then before the nerf on CoF the item rewards were already doubled so they nerfed them back and now we end up with 2x item rewards aswell. (However if you take into account the 1st day of the new CoF then we end up with just the same as 2 normal CoF runs.
So even if give you that, we end up with item rewards x2 in all stages and x4 in stage 15 (although pre nerf stage 15 would actually reward a random hero card with a 100% droprate)
So I do not know where you pull that x4 or x8 from Kemo.... but it is just not true. (I am vip 12 so pretty sure that's not it.)
gold rewards the same
2 x cof coins
and depending how you look at it x2 items
So just like I said yesterday, it's just a double coin event that comes with HUGE disadvantages. The risk/time is not worth the reward but the problem is, that even if you do normal cof you only get 1 run... as on my other account the reset didn't work and I deffo choose normal.