For who have CU, this is a gr8 chances to hatch more ultra rare animal by breeding those new rainbow animals with CU. For examples:
CU+TDTiger=sapphire cthulhul, opal octopus,...
CU+******s=peridot phoenix, quartz qualzaquot,...
CU+Rainbow dragon=ruby razorback, garnet griffin
In normal, if u breed CU with 1element (like pyro pony) u only get the animal u use to breed with the CU again (u may hatch new ultra rare animal but low chance). But if you combine 3 element together, you can't fail in 1element animal and you have higher chance to get those ultra rare animal. Anyway, rainbow dragon is the best wayto get new ultra rare animals because he is the rarest of all rainbow animal in this event. Try those combo and get more and more ultra rare creature. Actually it only use to make money and dislay in my forest lol because I don't wanna waste apples with them. Try toget all rainbow animals, good luck