My observation so far gave me a conclusion that those new element dragons (dark type or dragon with 'dark eye' symbol) weak against 'White-Blue' hybrids and 'Red' colour dragons. I beat Corrupt Skull with Playful (Red), Corrupt Darkwing with Banshee (White-Blue), and Corrupt Paper Lantern with Moonglow (White-Blue). A few minutes ago, I beat Corrupt Vinecrawler with my Fire dragon (Red) with only two magic attacks, first magic attack hit him critically (around 99%). That's my observation so far and maybe other players will have another different experience.