The last limited event dragon has been released, and you need 2 specific parents to breed a Mesmer dragon.
Masque + Scorn
This combination shares plant, fire, earth, cold, lightning & air. There are a lot of combinations.
226.75% in set percentages, so the 3% chance of Mesmer drops to 1.27%. 56 attempts required for a 50/50 shot, and with a 17.62 hour average fail time, it will take 41.11 days for that even money shot.
Cloning a Mesmer Dragon
It shares the same 6 elements, so Poison or Cactus is a good choice for cloning.