Hidden Sacrifice

Hidden Sacrifice is a process by which you can sac a face-down card with a non-zero Will as part of paying for a mana cost.

You cannot sac face-up cards or cards that have no Will this way. You cannot proactively sac valid cards this way outside of paying for a mana cost. The cards are sac'ed face-down and never summoned, so their effects are never activated (not even Shadowwalker effects). They are sent directly to the graveyard, so "When destroyed" effects are not triggered.