This section is for cards that can move cards from the discard pile to the hand, deck, or in play.
For Pokémon with Poké-Powers or attacks that attach Energy from the discard to Pokémon in play, refer to Energy Acceleration — Provides More Energy.
With the Holon Engine seeing widespread play, Pokémon Retriever is a natural complement. It can get back Pokémon that you discarded for Holon Supporters, or lost to KOs.
Pokémon Retriever has two modes: the fast 1 Pokémon to hand, and the slower 3 Pokémon to deck. Generally, if you need the Pokémon immediately you'll use the to-hand option, but if you can afford to wait, you can use the to-deck option. If you have a search effect ready (e.g. Pidgeot, Holon Mentor, Professor Elm's Training Method), you can use the to-deck mode and immediately search out what you put back.
Usually 1 Retriever is enough, but some decks that rely on Holon's Pokémon as Energy (e.g. Blastoise ex, Dodrio Fossils, Mew Lock) might want more.
This card is slower than Pokémon Retriever, as not only are you always locked into returning cards to the deck, it's also a Supporter, making it impossible to combo with Holon Mentor or Professor Elm's Training Method on the same turn.
Where Holon Farmer shines is in extreme resource grinds, such as against Camler. Camler will discard your Energy cards with Numel's Kindle and Energy Removal 2. Holon Farmer can return those discarded Energy (and even Holon's Pokémon) back to your deck. Camler can Push Away Holon Farmer, but you'll just get it back with Holon Transceiver.
Some decks are better equipped to search out the cards that Holon Farmer shuffled back. Meganium δ searches for 3 Pokémon from the deck when played, making Holon Farmer into Meganium a seamless 3-Pokémon recovery. Lunasol has Great Ball to get one Basic on the same turn that it plays Holon Farmer.
The first three of these cards generally have one juicy target: Pow! Hand Extension. Even though Sniff Out uses up your attack for the turn, you are far from vulnerable when you have Pow to move Energy away from their attacker, or to force in a Pokémon that can't attack.
The next use of Sniff Out is to recover more lock pieces than your opponent has answers for. If your opponent has 4 Windstorms and you have 4 Cessation Crystals or Crystal Beaches, you might be evenly matched, but if you can Sniff Out a lock piece even once, they're now in danger of using up all their Windstorms and not being able to answer your 5th copy.
Alakazam ☆'s Psychic Select has the same effect as Sniff Out, but requires Psychic Energy. Blastoise ex uses Alakazam ☆ more for Skill Copy than Psychic Select.
Gets a Supporter back.
Most often used with Mr. Briney's Compassion as a second copy of that card, with the option of turning into any other Supporter if you won't need to Briney twice.
Unlike the XY era, VS Seeker is not an automatic 4-of in RS-PK decks. Many decks don't even play a single copy! Why is that so?
Lack of Professor Sycamore. In XY, VS Seeker lets you retrieve Supporters that were discarded to Professor Sycamore. In RS-PK, there is no Professor Sycamore, and the Supporters that discard from your hand (e.g. Holon Supporters, TV Reporter) let you choose what to discard. You don't have to discard a vital 1-of Supporter to Holon Mentor and hope to subsequently draw into VS Seeker to get that Supporter back; you can just choose a less important card in your hand to discard.
Lack of variety in Supporter effects. In XY, powerful effects are balanced by being placed on Supporters, whereas in RS-PK, they are balanced by requiring coin flips. Compare Team Flare Grunt to Energy Removal 2, Lysandre to Pokémon Reversal, or AZ to Super Scoop Up. It makes sense that XY decks would want VS Seeker for flexibility: they can grab Professor Sycamore if they just need more cards, or an Energy Removal/Gust/Scoop Up/etc Supporter if they need that instead. In RS-PK, most Supporters merely draw/search for cards, and the argument for flexibility is lost. If you need more draw/search Supporters, you simply play more copies of those Supporters, or other Supporters with similar effects, instead of VS Seeker.
Form Variation switches Ditto with a Basic Pokémon from the discard pile.
The main advantage Ditto has over Pokémon Retriever is that you can put Ditto in play for a turn, then Form Variation it out and evolve the new Basic immediately. If you Retriever a Basic back and Bench it, you'd have to wait a turn.
Time Reversal recycles a card.
Often looped with Giant Stump and Pokémon Retriever, or Beating Wings Pidgeot.
Delta Support gets basic or δ Rainbow Energy cards back.
Requires the Holon Engine. The Energy it gets back can be discard fodder for Holon Supporters if necessary.
A staple in Blastoise ex, Flygon δ, or Meganium ex decks.
This card gets 2 Basic Energy from the discard pile or deck.
A 1-of in Rayler.
Upstream shuffles all Energy cards from your discard pile back into your deck, dealing a ton of damage if there are enough Energy cards.
Often played with Boost Energy, as it discards itself at the end of the turn, and you can topdeck it to pay for Tail Slap after using Upstream.
This Stadium gets basic Energy back from your discard pile.
Played in Blastoise ex, constructed specifically with no Special Energy cards (Holon's Pokémon don't count as Energy outside of play) so it can make use of Power Tree.
Magnetic Field is the classic Energy Retrieval effect, discarding 1 card for 2 basic Energy from the discard.
Played with Delcatty (it can even function as an attacker in that deck!) or Groudon ex.
Dig Up gets 2 Pokémon Tools back.
Often played with the intention of attacking, though not always early. 3 Energy for 70 damage is a good rate.