For Dedenne's "Dedechange" Ability, can I use it if I have no hand to discard?
Yes, you can. A hand of zero cards is still a hand, so you would discard nothing and then draw six cards.
Source: Unbroken Bonds FAQ (2019-04-19), TPCi Rules Team (2019-05-02)
When using Mr. Mime's "Pantomime" Ability, can I look at my prize cards when choosing which one to switch with the top card of my deck?
No, you cannot look at the prize card that you are switching out.
Source: TPCi Rules Team (2019-04-18)
Can I use Unown's "Farewell Letter" Ability to discard it from my bench if there are no cards left in my deck to draw from?
No, you cannot. The order of operations for Farewell Letter should be to draw a card first, then discard Unown. If you are unable to draw a card, then you cannot discard the Unown.
Source: TPCi Rules Team (2019-03-28)
What happens if I play Acerola or Super Scoop Up for a Pokemon with damage counters on it, but my opponent has Mr. Mime with the "Scoop-Up Block" Ability in play?
You can play the Acerola or Super Scoop Up, but its effect will be blocked and it goes to the discard pile without doing anything.
Source: TPCi Rules Team (2019-03-28)
Can I use Swampert's "Power Draw" Ability to discard a card from my hand if there are no cards left in my deck?
Yes you can. The first part of Power Draw is to discard a card from your hand, period. Then you do as much of the rest of the Ability as you are able to.
Source: TPCi Rules Team (2019-03-21)
Can I use Zebstrika's "Sprint" Ability if I have no cards in my hand?
Yes, since you can have a hand of zero cards you can use Sprint as long as there are cards in your deck to draw from.
Source: TPCi Rules Team (2019-03-21)
Can I use Zebstrika's "Sprint" Ability to discard my hand if there are no cards left in my deck?
No, you cannot. Discarding your hand is a cost not the effect, and you cannot use Abilities for no effect.
Source: TPCi Rules Team (2019-03-21)
Can I use Zoroark GX's "Trade" Ability to discard a card from my hand if there are no cards left in my deck?
Yes you can. The first part of Trade is to discard a card from your hand, period. Then you do as much of the rest of the Ability as you are able to.
Source: TPCi Rules Team (2019-03-21)
If I have Tapu Koko {*} and only one other Pokemon on the bench, can I use "Dance of the Ancients" to put 2 {L} Energy on that one other Benched Pokemon?
No, in this case, you can put only one {L} Energy on that Benched Pokemon. The second {L} Energy would have to go onto Tapu Koko {*}, but then gets discarded immediately anyway when Tapu Koko {*} goes to the Lost Zone.
Source: Team Up FAQ (2019-01-18), TPCi Rules Team (2019-01-31)
If I only have one {L} Energy in my discard pile, can I use Tapu Koko {*}'s "Dance of the Ancients" Ability to put it on one of my Benched Pokemon?
Yes, you would do as much as you can.
Source: Team Up FAQ (2019-01-18), TPCi Rules Team (2019-01-31)