(The Dredge deck archetype is based around the graveyard mechanic dredge, which is known to contain mostly incomprehensible nonsense.) In the case where the graveyard is good for you, please embrace your grave with open arms
You are given the option to either cast the Instant or Sorcery or cast the permanent from your hand
The card draw alone is enough reason to play this card, but in any control shell, you can make that second ability not even a downside and eventually win off the first ability
Instead, its better to swap them out for Prime Catcher, Night Stretcher, and two copies of Electric Generator to get the most out of your deck
Mega Greninja exs monstrous ability, Mortal Shuriken, makes this card an absolute monster in Water-type decks, while the artwork is too pretty to pass up in many full-art collections