If my Tyranitar GX knocks out an opponent's Glaceon GX with the "Freezing Gaze" Ability, does Tyranitar GX's "Lost Out" Ability turn on in time for it to send Glaceon GX to the Lost Zone?
Nope, Freezing Gaze is still active when Glaceon GX is KO'd, so Tyranitar GX does not get to use its Lost Out Ability.
Source: TPCi Rules Team (2018-12-27)
When I have seven cards in my hand, can I discard only one with "Sightseer"?
No, you cannot. You must discard until your hand has 4 or fewer cards when using Sightseer.
Source: TPCi Rules Team (2018-12-06)
Say my opponent has a Sudowoodo with the "Roadblock" Ability on his bench, but it's currently disabled due to my active Alolan Muk's "Power of Alchemy" Ability. If I have five Pokemon on my bench when Alolan Muk gets KO'd and "Roadblock" becomes enabled, do I have to discard one of my five benched Pokemon before promoting a new Active Pokemon or not?
When you remove your Active Pokemon after resolving all effects that caused it to be KO'd, you must replace it immediately before resolving any other new effects that take place.
Source: TPCi Rules Team (2018-12-06)
If my opponent used Gardevoir EX's "Shining Wind" attack to gain "no Weakness" and I play Pokemon Ranger when it is my turn, does their Gardevoir EX have a Weakness again?
Yes. The ruling about effects on Weakness and Resistance not being ignored has to do with damage calculations [see "General Gameplay -> Weakness and Resistance" section for reference], not about whether a Pokemon HAS Weakness or Resistance. Pokemon Ranger removes attack effects, including this one; so yes, Gardevoir EX would have Weakness again after using Pokemon Ranger.
Source: TPCi Rules Team (2018-11-15)
If I use Sylveon's "Wink Wink" attack to have my opponent discard Ilima, can I use Victini's "Victory Star" Ability to force my opponent to re-flip their coins?
Yes, you can. If your opponent flips a coin as part of your Pokemon's attack, you can use "Victory Star" to force them to re-flip those coins; but keep in mind you will have to re-flip your coins for Ilima too.
Source: TPCi Rules Team (2018-11-15)
How does Slaking's "Lazy" Ability or any other form of Ability denial that only applies to Pokemon "in play" interact with Abilities like Giratina's "Distortion Door" Ability that puts a Pokemon card from the discard pile onto your bench?
Since Distortion Door happens when Giratina is not in play, you can use it to put Giratina onto the bench regardless of Lazy or other similar Abilities. You also get to put the damage counters onto your opponent's benched Pokemon too, because you must complete the action of Distortion Door prior to it being shutoff due to Lazy.
Source: TPCi Rules Team (2018-11-15)
Is there any way to clear the effect of Lusamine {*}?
No, however any attacks that ignore effects on the Defending Pokemon would get through its effect.
Source: Lost Thunder FAQ (2018-10-20), TPCi Rules Team (2018-11-01)
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)
If Blacephalon GX uses its "Mind Blown" attack to discard a Beast Energy as one of the Fire Energy discarded, does it still get the +30 damage bonus from Beast Energy?
Yes, it does. The energy cards are chosen, then Damage is calculated before the cards are sent to the Lost Zone.
Source: TPCi Rules Team (2018-11-01)
Does using Lugia GX's "Lost Purge GX" attack count as KO'ing a Pokemon?
No, it does not. You are moving the opponent's Active Pokemon and all cards attached to the Lost Zone, and since it does not count as a KO you don't get to take any prizes for it.
Source: Lost Thunder FAQ (2018-10-20), TPCi Rules Team (2018-11-01)