If I use Nihilego's "Nightcap" attack to copy my opponent's Pikachu & Zekrom GX's "Tag Bolt GX" attack, does it need 6 {L} attached or just an additional 3 {L} attached in order to get the bonus effect?
Nightcap replaces the normal amount of energy required by the opponent's attack with a single Psychic Energy cost. So for Tag Bolt GX, Nihilego would need 4 total Energy (1 to pay for Nightcap + 3 extra Lightning) to get the bonus effect.
Source: TPCi Rules Team (2019-05-02)
If I use Ditto's "Copy Anything" attack to copy one of my opponent's Tag Team GX attacks with a bonus effect for extra energy attached, do you count the extra energy starting at Energy #2, or after you take into account the "necessary Energy to use that attack"? For example, if it copies Pikachu & Zekrom GX's "Tag Bolt GX" attack, does it need 6 {L} attached or just 4 in order to get the bonus effect?
You count based on the required energy that normally has to be attached for the attack. So for Tag Bolt GX, Ditto would need 6 {L} energy attached to get the bonus effect.
Source: TPCi Rules Team (2019-04-18)
When using Hoopa GX's "Devilish Hands GX" attack, can I keep choosing a Pokemon that would already be Knocked Out by previous choices, or do I have to choose a different Pokemon once I have done enough damage to KO the first one?
You make all 6 choices before doing any damage; so if you wish, you can do more damage than you need to a Pokemon in order to knock it out.
Source: Team Up FAQ (2019-01-18), TPCi Rules Team (2019-01-31)
If my opponent has no benched Pokemon, do I do 50 damage to their active Pokemon when I use Nidoking's "Drag Off" attack?
No. Damage is only done to the "new Active Pokemon". If there is no switch, then no damage is done.
Source: Team Up FAQ (2019-01-18), TPCi Rules Team (2019-01-31)
When I use Zangoose's "Head Hunt" attack, do I have to put all Pokemon I find into my hand, or can I choose to discard some or all of them?
Since you get to choose which Pokemon to reveal, you can choose to discard some or all of them.
Source: Team Up FAQ (2019-01-18), TPCi Rules Team (2019-01-31)
If my opponent Knocks Out my Active Pokemon and I promote my Zapdos to be Active after the attack, do I get the bonus 70 damage for "Thunderous Assault"?
No. In this scenario you promoted the Zapdos while it was still your opponent's turn. In order to get Thunderous Assault's additional damage it would have to become Active during YOUR turn.
Source: Team Up FAQ (2019-01-18), TPCi Rules Team (2019-01-31)
When I use Mimikyu's "Copycat" attack, do I need to have the same required energy as the opponent's previous attack?
No, you only need whatever energy is required on Mimikyu in order to use its Copycat attack. However, if the attack requires you to do something with a particular type of energy you don't have, you cannot use that part of the copied attack.
Source: Team Up FAQ (2019-01-18), TPCi Rules Team (2019-01-31)
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)
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)