If opponents are out of said options, nine damage is a lot to spread around and it's nearly impossible to block
It is the only unlimited Pokmon-e Series 1 card we have definitive proof of its source, and in reality its actually pretty common
Another variant, and the one that's more relevant here, jams in as many 0-cost artifacts as possible and plays Weapons Manufacturing, spitting out a load of Munitions tokens
In addition, they cite the hard-to-read text and mana costs as potential concerns for new players unfamiliar with the cards original printings
Speaking of Black Kyurem, worth mentioning the art too, it may not be up to the level of most of this thread, but as someone who loves Zekrom but usually hates Black Kyurem, my first reaction towards it was that it's very cool