Double faced cards multiple transform triggers
Several points for the first question:


Elusive Tormentor's ability is not triggered, it is activated. 
Discarding the card is not part of its effect, but part of the cost, and there is no limit to how often you activate that ability. 
Even if it was part of the effect, you could still activate the ability several times and discard several cards, because the discard and the flip would be separate effects. If one effect of a spell or ability gets prevented or replaced somehow, the other effects are not affected.