If a Pokemon was attacked with Lunala GX's "Moongeist Beam", does that block Mallow & Lana from healing it?
The first part of Mallow & Lana says to switch your Active Pokemon with one of your Benched Pokemon. When your Pokemon is switched the effect of Moongeist Beam is removed, so then you can heal the Pokemon once it is on the Bench.
Source: TPCi Rules Team (2020-02-27)
Say my opponent uses Trevenant & Dusknoir GX's "Pale Moon GX" attack on my Keldeo GX with "Pure Heart" while Power Plant stadium is in play. If I replace the Power Plant with another stadium during my next turn, does Keldeo GX get knocked out at the end of the turn or not?
If Keldeo GX remains the Active Pokemon it will be Knocked Out. Keldeo GX's Pure Heart Ability *prevents* effects, but it does not *remove* existing effects. If an attack like Pale Moon GX places an effect directly on Keldeo GX, that effect cannot be removed by reactivating Pure Heart; in other words, effects that are removed when returning to the Bench can't be removed by Pure Heart.
Source: TPCi Rules Team (2020-01-09), TPCi Rules Team (2020-02-06)
If I use Cramorant V's "Beak Catch" attack, can I choose to fail to get any cards from my deck?
Only if there are no cards left in your deck. Since you can get any type of card, and it is known that you have cards in your deck, you must take at least 1 card if you are able to.
Source: Sword & Shield FAQ (2020-01-24), TPCi Rules Team (2020-02-06)
If I used Sandaconda's "Coil" attack and my opponent retreats their Active Pokemon, do I still do an extra 120 damage to the new Defending Pokemon?
Yes. The attack states "your opponent's Active Pokemon". That is referencing any Pokemon that is in their Active Spot.
Source: Sword & Shield FAQ (2020-01-24), TPCi Rules Team (2020-02-06)
What happens if I use Morpeko V's "Electro Wheel" attack but I don't have any Benched Pokemon?
You still have to discard an Energy if you can, but since there are no Benched Pokemon to switch with, Morpeko V stays in the Active Spot.
Source: Sword & Shield FAQ (2020-01-24), TPCi Rules Team (2020-02-06)
Can I use Grapploct's "Octolock" attack to a new Defending Pokemon if the previous one switches out?
If you use the attack again, yes. You just can't apply more than one Octolock effect to the same Defending Pokemon.
Source: Sword & Shield FAQ (2020-01-24), TPCi Rules Team (2020-02-06)
Grapploct's "Octolock" attack says its effect can't be applied more than once. What does that mean?
It means that if the Defending Pokemon is already under the effect of Octolock you cannot do it again for an additional {C}{C} cost. In other words, it does not stack.
Source: Sword & Shield FAQ (2020-01-24), TPCi Rules Team (2020-02-06)
Say I have Keldeo GX already in play, and my opponent uses Latios GX's "Clear Vision GX" attack with Power Plant in play. If I play a different Stadium to get rid of Power Plant, can I use Keldeo-GX's "Resolute Blade GX" attack now?
Yes, you can. When Power Plant is removed Keldeo GX's Pure Heart Ability turns back on, and Keldeo GX is no longer hit by the global effect of Clear Vision GX. If an attack does not place an effect on Keldeo GX directly, like an attack that puts an effect that isn't removed when returning to the Bench, it can be removed by reactivating Pure Heart.
Source: TPCi Rules Team (2020-02-06)
If a player has some face up prize cards from using Blacephelon's "Blazer" attack and then takes a multi-prize knockout, do they take their prizes one at a time or must they take all of them at once?
Whenever you take more than one prize in a single action, each prize can be taken one at a time.
Source: TPCi Rules Team (2020-01-09)
Does Channeler negate the effects of Arceus & Dialga & Palkia GX's "Altered Creation GX" attack?
It depends on who is playing the Channeler. If the player who used Altered Creation GX uses Channeler then the effects are removed; the player's Pokemon no longer do +30 damage and the player does not get to take any extra prizes from the effect. However, if the player's opponent plays Channeler, then Altered Creation GX effects are not removed as they reside on the other player (who did not play Channeler).
Source: TPCi Rules Team (2020-01-09)