The Spells/Traps that can destroys cards are "Dark Hole" (monsters), the already mentioned "Hunting Ground" (Spell/Trap), "Mystical Space Typhoon" (Spell/Trap), "Smashing Ground" (opponent's monster with the highest DEF), "Bottomless Trap Hole" (opponent's monster with 1500 or more ATK), "Icarus Attack" (2 cards), and "Mirror Force" (opponent's monsters in Attack Position)
Yes, the effect reads "you may return [...] to your hand," therefore you may choose to not return cards to your hand
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The big old load of text on this card reads, Whenever an opponent sacrifices a nontoken permanent or discards a permanent card, you may put that card from a graveyard onto the battlefield under your control. Its just a good way to keep getting more value out of your discard and sacrifice effects, and youve got a lot of them to use
Then theres Support cards which are similar in effect to Item cards, though you can only play one per turn