Can I use the Supporter "Copycat" when my opponent has no cards in his or her hand?
Yes, you can. Shuffle your hand into your deck, but don't draw any cards.
Source: HeartGold & SoulSilver FAQ (2010-02-11), PUI Rules Team (2010-02-11)
Can I use cards that search for a Pokemon, like "Bebe's Search" or "Poke Ball" to get a Pokemon LEGEND card from my deck?
Any effect that lets you search your deck or discard pile or do something from your hand with "a Pokemon" will let you use that effect on one half of a Pokemon LEGEND set, but not both halves.
Source: HeartGold & SoulSilver FAQ (2010-02-11), PUI Rules Team (2010-02-11)
If I use Pokemon Communication to put a Pokemon into my deck, am I allowed to voluntarily fail and choose to take no Pokemon out of my deck?
The contents of your deck is not public knowledge so the deck search can fail, even if you've just put a Pokemon into the deck.
Source: PUI Rules Team (2010-02-04)
Can I use Rare Candy to evolve from Dome Fossil to one of the Kabutops from older expansions that evolve from Mysterious Fossil?
Since Kabutops can evolve from Kabuto of any expansion, you may use Rare Candy to evolve either Dome Fossil or Mysterious Fossil into any Kabutops, regardless of expansion.
Source: PUI Rules Team (2008-05-22)
I have never had this come up and I can't find anything saying you can't, but can you attach 2 Technical Machines to the same Pokémon at the same time?
There are no restrictions on TM's that say you cannot, so yes you can.
Source: PUI Rules Team (2006-01-26)
Could I play a trainer if it's obvious that it will have no effect (i.e. Life Herb on a Pokémon without any damage and with no Special Conditions on it)?
No, you cannot play a card if it is obvious that you cannot do what the card is supposed to do at that moment.
Source: PUI Rules Team (2005-09-22)
If you use Rare Candy to evolve a Pokémon, and the evo card has a "Coming into Play" Pokémon Power (such as Dark Crobat), does that coming into play power get activated?
Using Powers, Attacks, or Trainers that let you put a Pokémon in the game from your hand will allow coming into play Powers to activate. This is a reversal from previous rulings.
Source: PUI Rules Team (2003-10-23), PUI Rules Team (2005-04-14)
Can I evolve Dratini in play to Dark Dragonite by using Rare Candy?
Yes. [This is true as long as there is a normal evolutionary path between the basic and the Stage 2 "Dark" Pokémon.]
Source: PUI Rules Team (2005-02-10)
Does Rare Candy override evolution-preventing effects such as Fossil Aerodactyl's "Prehistoric Power"?
Yes, you can use Rare Candy when Aerodactyl's Prehistoric Power is in play.
Source: PUI Rules Team (2003-09-18), PUI Rules Team (2004-07-22)