Because Xyz Summoning removes monsters to turn them into materials, you can Xyz Summon onto a field where every monster slot has been filled
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
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
Monsters that can be summoned from the current EX Deck are excellent across the board
Assembling a full set of TKN4 has been something collectors have struggled with, as its a very difficult undertaking