Creatures you control can tap to produce at least ({3} magic symbol) ({R} magic symbol) .
Steps
Activate all mana-producing creatures you control by tapping them, adding at least ({3} magic symbol) ({R} magic symbol) .
Cast Stonecoil Serpent by paying ({0} magic symbol) .
Stonecoil Serpent enters the battlefield and dies as a state-based action due to having zero toughness.
Intruder Alarm and Mortuary trigger.
Resolve the Intruder Alarm trigger, untapping all creatures.
Resolve the Mortuary trigger, putting Stonecoil Serpent on top of your library from your graveyard.
Activate Hidetsugu's second ability by paying ({2} magic symbol) ({R} magic symbol) and tapping it, exiling Stonecoil Serpent from the top of your library and allowing you cast it this turn.