If a creature that's no longer on the battlefield is instructed to explore, it can, as long as the spell or ability doing that resolves
fake cards are pretty much always cards that have a secondary market value, you don't have to worry about your Giant Sharks being faked as it's simply not worth it
The new theory presented by @pokemonrevolution suggests sheets are stacked on top of each other before the 1st edition stamp ink was dry, causing both the imprints at the back of the cards, as well as the Grey stamps
Final Thoughts Pokemon TCG Pocket is a faithful mobile card game adaptation thats better for shiny digital collections than thrilling monster battles.
If you still havent found your cards, its time to inform the Tournament Organizer of your loss and check out the Lost and Found
Fumulus, the Infestation Fumulus, the Infestation helps out sacrifice decks by turning any real creatures you sacrifice into a second body for cards like Goblin Bombardment and Ashnod's Altar