Hi,
I’ve noticed that now it’s possible to destroy creatures having “Prevent damage” with cards like Grip of Desolation or To the Slaughter but it’s not possible to destroy such creatures with Ob’s 2nd skill. At least it couldn’t destroy Archangel Avacyn.
They did something. Before it wasn’t possible to destroy Avacyn with “Destroy” card. Now it is … but not with OB’s 2nd skill that should has effect same as those cards.
They did that a while ago, they just never did it for Ob’s 2nd skill (Torment). The bug was posted months ago. No response to it still.
Ob Nixilis’ 2nd ability is busted anyway.
It doesn’t destroy the Undergrowth Champion. It states destroy but it removes a -1/-1 instead.
Look at the date of that post in my link. 
Reiterating. Either the devs know it exists and don’t care, they don’t know it exists, or they know it exists and can’t fix it for some reason (but won’t/can’t communicate to players). Either way, they’re doing a bad job in regards to bug fixes.