(Hollow Retreat isn't a spell.)
Hollow Retreat enters the battlefield tapped.
, : Look at target player's hand.
: Add or to your mana pool.
: Add to your mana pool. Put Hollow Retreat on top of your library.
, 
: Look at target player's hand.: Add 
or 
to your mana pool.: Add 
to your mana pool. Put Hollow Retreat on top of your library.
