Fun fact: Charnel Troll has a template that hasn’t been used before. (Well, technically on one un-card, but I’m not about to use that for precedent!) This has led to a question of whether the “otherwise” on the trigger means “if you don’t” or “if you can’t”. This matters because the former is a trigger with a default action, while the latter is an ordinary trigger. If it’s a default action, then missing the trigger means that the Troll will meet an untimely death when it’s discovered.
After discussion with Wizards, the pro-Troll faction has emerged triumphant. It gets to live! Because the first part is mandatory, the “otherwise” is directly tied to it and not a generic catch-all for when it doesn’t happen. The Troll has no default action as part of the trigger. (Note that if the opponent puts the ability on the stack, you can’t discard cards to save it; you must remove a card that was there when the ability would have resolved correctly).
We’ll look into updating the definition to account for this new template in the next IPG release. In the meantime we return to our more usual trolling.