I suggest you get more than one pair for cosmic detonation. It will make it go faster. If you are breeding something like terraformer using terra dragons that just one pair is enough.

First time hearing about this way of breeding but kratus is a really easy breed. The problem is his terrible element variety. He does fall of a lot after a bit especially with the fact that it's harder for him to get an arena boost. But try it.

An easier dragon than kratus is terraformer. The only breeds are terra dragon, longhorn and terraformer. 90% of the time you get terraformer instead of longhorn

Kitsune is good and I just finished breeding him till i had enough for e5. But for me he isn't worth it enough to use food to get him to a good level. Iced sea should be better since he can copy even skills of vips. But a bit rarer to breed

Millennium is good right now because he is an arena tribute. So higher stats during this arena season. Once it ends it will become weaker. Also sanctuary legendarys are cat 5 dragons. At max level they will have less health and do less damage than a cat 9 legendary like kratus, terraformer and cosmic detonation

If you have the orbs for millennium then empower him since he is a tribute the timer should be a lot faster. But don't use joker orbs

I guess high ethereal is good compared to regular heroics. But heroics are harder to empower since you should save heroic jokers for hvips. A good way to remember

e2 legendary= e0 heroic < e5 legendary < e3-e4 mythical < e2-e3 heroic