The end step (and every phase and step in an MTG turn, for that matter) is mandatory, meaning you cant choose to skip it
A devastating power if true, as it means you could take all the Energy from a nearly-beaten Pokemon and give it to a freshly deployed Articuno or Gyarados
Pricing as if the whole sale price is yours is how thin-margin cards turn into losses
Generally, the value of a GX card can range anywhere from a few dollars to several hundred dollars or even more for particularly rare or sought-after cards
Cards like Wound Reflection and other amplifications cards will help to get you the win, and considering the card advantage Kefka gives, you can run combo wins pretty reliably
While not always as good and reliable as a Shock it does have a higher average range which is not something we can often say about one mana removal cards outside of red