Sadly I do not have video footage because I was playing off-stream but this bug is so massive it INSTANTLY caused me to lose the game. Let me try to explain the board state. It was my 3rd turn, and my opponent (Paladin) had the following in play: The hidden secret [Oh My Yogg!] and two 2/3 minions of no particular importance, though one of them being [Redscale Dragontamer]. I played [Flame Ward] and that triggered [Oh My Yogg!] to change my [Flame Ward] into a [Mark of Nature]. Well, ok I thought, I hope it doesn’t give +4 Attack or the game might become hard for me. It was far worse. Not only did it cast [Mark of Nature], it cast the spell THREE TIMES for a total of +8 Attack and +4 Health and Taunt. My opponent now had a 10/7 Taunt Redscale Dragontamer on turn 4. I don’t need to explain how that causes me to immediately lose.
So the presumed bug is as follows. When [Mark of Nature] is cast as a random choice from [Oh My Yogg!] it is for some reason cast THRICE. The result is assumedly replicable, and I would try to but I don’t want to waste my time when hearthstone devs can forcibly replicate it themselves.