Honestly, at 3 time, fate egg is a darn near useless card. I suggest lowering the cost to 1-2. It's not like the cost lowering would suddenly make all the rainbows spam them in their deck; they would still probably be relatively weak. But it would be useful for speed mono time; kinda like Giant Frog in speed life decks.
It's an easy fix that could be quickly included with the next update, if the game is coded like I think it is.