If a player attacks with Gengar & Mimikyu's "Horror House GX" attack, will the opponent be able to attach an energy card from their hand via Eternatus V's "Power Accelerator" attack or Shadow Rider Calyrex VMAX's "Underworld Door" Ability?
No, you can't do anything that takes a card from your hand and puts it in the play area after your opponent uses Horror House GX. That includes Abilities, card effects, and attack effects.
Source: TPCi Rules Team (2021-07-01)
Say I played Mimikyu V and used its "Dummy Doll" Ability on my turn. Then on my opponent's next turn, they play a Path to the Peak stadium. Does that cancel the effect of "Dummy Doll"?
Since the Dummy Doll Ability activated and placed an effect before Path to the Peak came into play, its effect remains.
Source: TPCi Rules Team (2021-07-01)
Can I use Porygon-Z's "Crazy Code" Ability to attach Impact Energy to a Pokemon that isn't a Single Strike Pokemon?
Yes you can, but then it would get discarded immediately. However, if that Pokemon was Poisoned, Impact Energy would remove the Special Condition.
Source: TPCi Rules Team (2021-07-01)
If I have Greedent in play, will its "Brazen Tail" Ability prevent Faba from putting my Special Energy into the Lost Zone?
No, Brazen Tail does not protect against the Lost Zone.
Source: TPCi Rules Team (2021-07-01)
Can I use Houndoom's "Single Strike Roar" Ability to search my deck for the special energy card Impact Energy?
No, you cannot. Single Strike Roar is only able to target a specific card named "Single Strike Energy". Although Impact Energy is a "Single Strike" Energy card, it is not "Single Strike Energy".
Source: Chilling Reign FAQ; TPCi Rules Team (2021-06-17)
Can I use Shadow Rider Calyrex VMAX's "Underworld Door" Ability if there are no cards left in my deck to draw from?
Yes, you can. Attaching Psychic Energy is the main effect of the Ability, which means it can be used even if you have 0 cards in your deck.
Source: Chilling Reign FAQ; TPCi Rules Team (2021-06-17)
If I use Shadow Rider Calyrex VMAX's "Underworld Door" Ability, do I have to draw 2 cards?
Yes, it is not optional (it does not say "you may"). You must draw 2 cards if you are able to; you can only draw a single card if it's the last card in your deck.
Source: Chilling Reign FAQ; TPCi Rules Team (2021-06-17)
Does Passimian's "Throwing Coach" Ability work if my Active Pokemon's attack doesn't do any damage to the opponent's Bench?
No, Throwing Coach only adds +30 more damage when you actually do damage to your opponent's Benched Pokemon. In other words, you have to do some bench damage in order to have "+30 more" done.
Source: Chilling Reign FAQ; TPCi Rules Team (2021-06-17)
Can I use Galarian Slowking's "Mysterious Potion" Ability on a Pokemon that isn't damaged?
Yes, you could try to damage your own Pokemon if you really wanted to.
Source: Chilling Reign FAQ; TPCi Rules Team (2021-06-17)
Can I choose to search my deck for zero cards if Gengar with the "Last Gift" Ability is Knocked Out (for example, if I don't want to empty my deck)?
Since the search is not optional (it does not say "you may") you must take at least one card if you are able to.
Source: Chilling Reign FAQ; TPCi Rules Team (2021-06-17)