Ojimaru said:
I'm a little confused as to whether you have to reveal all cards that are searched from your deck, graveyard or RFG zone via card effect. For example, do I have to show my opponent the Giant Rat I moved from my deck to my hand with Sangan's effect? How about Ancient Gear Drill's effect?
Any time you search your Deck for a card that has a specific card type mentioned in the effect text, you must show your opponent.
The only time you are not required to reveal the searched card is when the effect allows you to remove "any" card from your Deck, as "any card" can be anything, while "any SPELL card" must be revealed.
Des Feral Imp allows you to remove any card from your Graveyard and return it to your Deck. You do not have to reveal what type of card you removed (unless your opponent chains to his effect with a card like Disappear, or D.D. Crow).
Magician of Faith allows you to remove a Spell Card from your Graveyard and return it to hand. You must show that you removed a Spell Card, which means you do NOT just show that it is "green". You must show the full card face, with all information visible.
If you activate Miracle Dig, you are only allowed to return 3 Monsters to your Graveyard, and again, you must show the full card face, as the cards are specifically mentioned by the effect text.
Primal Seed only says to return two cards to hand that are removed from play, so you do not have to reveal the cards to your opponent.
Different Dimension Capsule also does not require the card to be revealed.