Using sniping techniques and cards like Team Magmas Secret Base, Mega Tyranitar EX can easily deal damages exceeding 760 to the opponent, given there are adequate damage counters placed on the defending pokemon
It is, in general, just a poorly designed card and one of the main reasons as to why Dragon Rulers were such a power house
Assembling a full set of TKN4 has been something collectors have struggled with, as its a very difficult undertaking
Sometimes, when you don't go straight to the event site of your partner (marked with "!"), and you visit another places and duel with another character's (in the same day), the completed Heart of your partner will vanish, the mark of the event will disappear in the map and the Game will not let you fill that Heart again (regardless of how many positive interactions you do with him/her in the next days via gifts.) To rectify this, you need to invite that person to the tag team duel tournament
There are much cheaper alternatives, after all, if you're playing with a Green deck: you can have an Allosaurus Shepherd, Destiny Spinner, or Prowling Serpopard for half mana or less cost than Chimil
If you dont mind getting a little messy, this card could be a good source of counters