Not once per turn, no reset on damage, just once
Play the usual TeraZard line, evolve to put 2 Fire on Active and 1 on a backup Mander, take some knockouts, then before the first TeraZard gets KO'd (or if you have other ways to keep 4 energy in play, which Zard/Pidgeot should be able to do), evolve to a MegaZard and take out any opposing megas by dealing 380 damage
Anybody interested in making the most of this card, has to be sure to play enough Druids
(Plus they get to essentially draw a card as a prize for killing your guy
There are plenty of staple cards for you to play in your Elf deck, but there are also some unique cards that you might not think to include in your deck-building process
It effectively blocks all the nasty threats of the format, such as Sprite Dragon, Arclight Phoenix, and Stormwing Entity