It seems breeding in the cave can be more advantageous than breeding on the island in certain situations.
I did an analysis using the Gold Olympus dragon as the target:
As you can see, one would wait a less amount of time on average with the Cave when missing on the Gold Olympus (because the Island would give a greater chance of giving you an unwanted Epic with a higher breeding time).
I got the percentages from the excellent Breeding Sandbox: *** Edited ***
It appears Epics, Gemstones, Opposites & Limiteds have fixed percentages then the remaining percentage from 100% is evenly divided amongst the Commons (Uncommons become Commons when there are 3 or more results). So the amount of miss results have no relevance, since there will always be the same odds of getting your Rare dragon no matter what.
I question why there isn't an increased percentage for the Gold Olympus or Rainbow when using the Island.
The Air + Crystal/Quake combo is the Sandbox' recommended combo, but I don't understand why. It sure appears nicer with the much fewer results, but according to the Sandbox' Combo Finder, the Air + Crystal/Quake combo has only the 4th best time rating, whereas the Ash + Dodo (et al.) combos have the 1st best time rating.
Please comment/correct, thanks.
Edit: Actually, Blazing + Crystal et al. is usually the #1 time saving combo for Olympus with Avg Miss Times of10.847hr (cave) & 12.821 (island). However, it is rock bottom right now thanks to the limited Solar Eclipse result.
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