What happens if I put a Keldeo GX with "Pure Heart" Ability into play after my opponent has used Latios GX's "Clear Vision GX" attack? Would my Keldeo GX be able to use its "Resolute Blade GX" attack or not?
As long as the Pure Heart ability is not blocked or turned off when Keldeo GX comes into play, it would be unaffected by Clear Vision GX.
Source: TPCi Rules Team (2019-12-05)
If I have a single Rainbow Energy attached to Moltres & Zapdos & Articuno GX, can I use the extra effect of its "Sky Legends GX" attack?
No, even though Rainbow Energy provides all energy types simultaneously, it only provides one unit of energy. You can use it for either the Fire or the Water or the Lightning, but you still need additional units of energy for the other required types.
Source: TPCi Rules Team (2019-11-14)
Can I use Mimikyu's "Copycat" attack to copy an attack like "Flare Strike" that says "this Pokemon can't use Flare Strike during your next turn" and then on my next turn use "Copycat" to copy that same attack again?
Attacks like Flare Strike put an effect on the Pokemon that prohibits using that particular attack on your next turn. But Mimikyu's Copycat attack doesn't have that restriction; so yes, you can use Copycat to copy Flare Strike multiple turns in succession.
Source: TPCi Rules Team (2019-11-14)
If my Pokemon is Confused, can I use the effect of Will to choose Heads for the Special Condition?
No, that isn't something that Will can affect.
Source: Cosmic Eclipse FAQ (2019-10-18), TPCi Rules Team (2019-10-31)
If my opponent used Magnemite's "Mirror Shot" attack last turn, can I use the effect of Will to choose heads for the effect of the attack?
Yes, that is considered an effect of an attack, so that works.
Source: Cosmic Eclipse FAQ (2019-10-18), TPCi Rules Team (2019-10-31)
You can do any part of Red & Blue as long as there's a Pokemon in play that can evolve into a Pokemon-GX AND there's at least 1 card in your deck.
Source: Cosmic Eclipse FAQ (2019-10-18), TPCi Rules Team (2019-10-31)
You can play Misty & Lorelei for the base effect as long as there's at least 1 card in your deck. You can always play it by discarding 5 cards from your hand.
Source: Cosmic Eclipse FAQ (2019-10-18), TPCi Rules Team (2019-10-31)
When I play Misty & Lorelei, can I discard one or more of the 3 {W} energy I searched for as part of the 5 cards discarded to get the re-use of my GX attack on this turn?
No. You have to discard 5 cards "when you play this card". That is before you search for the {W} energy cards.
Source: Cosmic Eclipse FAQ (2019-10-18), TPCi Rules Team (2019-10-31)
Can I use the second part of Misty & Lorelei to discard 5 cards if I have not already used my GX attack for the game?
No, you cannot. If you haven't used your GX attack yet, you can't discard 5 cards from your hand.
Source: Cosmic Eclipse FAQ (2019-10-18), TPCi Rules Team (2019-10-31)