Cards like these are exceptionally rare, with the drop rate of these cards averaging out to being just one per three to four cases (though that number will vary from set to set)
But honestly, the mechanical strength of the card outweighs this minor quibble
Its very easy for Watchful Radstag to get out of control if no one deals with it early
However, in my opinion, the Basic Thundurus is probably the best backup card in the deck allowing you to deal damage as well as attach Lightning Energy to a Benched Pokemon, in one single attack
Have lots of artifacts in play, mill yourself, get more artifacts back from the graveyard, repeat
Today marks the beginning of the second week of preview season, and my focus now shifts to another main part of Dominaria, Legendary creatures