Can I play Kahili if there's only one card left in my deck?
If you can draw at least 1 card from your deck, you can use Kahili and do the coin flip part. But if you can't draw any cards, you can't use it.
Source: Lost Thunder FAQ (2018-10-20), TPCi Rules Team (2018-11-01)
Can I play Fiery Flint if I only have 1 card in my hand to discard?
No, you must be able to discard 2 cards in order to use Fiery Flint.
Source: TPCi Rules Team (2018-09-27)
Does using Beast Ball count as "taking a prize" for the purpose of calculating damage for Stakataka GX's "Assembly GX" attack?
No, it does not. You are switching cards, not taking a prize.
Source: TPCi Rules Team (2018-08-16)
Sky Pillar says, "Prevent all effects of the opponent's attacks, including damage, done to Benched Pokemon (both yours and your opponent's)". So does this mean if I use an attack like Zapdos' "Raging Thunder" that I do not apply the bench damage to my own Pokemon?
No, only bench damage done from an opponent's attacks is prevented by Sky Pillar. If your attack does damage to your own Benched Pokemon it is not prevented.
Source: TPCi Rules Team (2018-08-09)
If I use Gladion and choose to put Jirachi {*} into my hand, can I use Jirachi {*}'s "Wish Upon a Star" Ability?
Sorry, but Wish Upon a Star only triggers when you are taking it as a face-down prize card, not when you are trading it with another card.
Source: TPCi Rules Team (2018-08-02)
Can Apricorn Maker be used to search for the Trainer "Bursting Balloon"? Taking the card literally, Bursting *BALL*oon contains the exact same "Ball" as given on Apricorn Maker.
Of course not, don't be silly! You can only search for cards like Poke Ball, Ultra Ball, Beast Ball, etc.
Source: Celestial Storm FAQ (2018-07-20), TPCi Rules Team (2018-08-02)
Can I use Wally or Evosoda on a Snorlax to search my deck, even though there is {currently} no evolution of Snorlax?
No, there has to at least be the possibility of a valid evolution in order to use this card. Sorry.
Source: TPCi Rules Team (2018-07-26)
Can I use Wally or Evosoda to search my deck for a card that is not in the current tournament format? For example, could I use it on Raichu to search for a Raichu BREAK after it rotates out?
Yes, you can. Even though a card may not be in the tournament format it still exists and can be searched for even though it is known to fail.
Source: TPCi Rules Team (2018-07-26)