How to breed a winter dragon

For cases such as the above, where a hybrid dragon includes opposing element types, it is not possible to use basic dragons. Since the basic dragons are opposites, they will not breed, and that is why they get greyed out as options. In order to breed these dragon types, it is necessary to choose at least one hybrid dragon in the pairing. For best chances, pairing a basic with a hybrid will reduce the number of other potential unwanted dragon types that can result. So for example by this logic Fire + Lichen (Cold hybrid) would be a better choice to attempt Blue Fire than Brass (Fire hybrid) + Lichen (Cold hybrid).

For a Plasma Dragon all you need is a Lightening Dragon and a Water hybrid, or a Water Hybrid and a Lightening dragon. Water + lightening alone doesn't work since they can't breed.

Anything like Iceberg + Lightening or Water + Cactus should work well. They have an incubation time of 16 hours.