Treebeard (hero) + song of mocking

By Courchevel, in Rules questions & answers

Hello all

Again a grey area in my understanding of the rules :

Are we able to redirect to another hero (via song of mocking) the damage that treebeard (hero) has taken to boost itself ?

Same question with Dori ?

My confusion comes from something that I read (and I cannot find) which basically stated that when the text of a card was "do x to do y", you cannot really do y unless x was fulfilled.

So that if something would cancel the x, you would not be able to do y.

Again, thanks in advance.